diff --git a/src/bigint/native.mjs b/src/bigint/native.mjs
index dc12d9e..6458912 100644
--- a/src/bigint/native.mjs
+++ b/src/bigint/native.mjs
@@ -1,9 +1,11 @@
 import gcdType from '../generic/gcdType.mjs'
+import {identity} from '../generic/identity.mjs'
 
 export * from './Types/bigint.mjs'
 
 export {add} from './add.mjs'
 export {compare} from './compare.mjs'
+export const conjugate = {bigint: () => identity}
 export {divide} from './divide.mjs'
 export const gcd = gcdType('bigint')
 export {isZero} from './isZero.mjs'
diff --git a/src/complex/add.mjs b/src/complex/add.mjs
index 1afd22f..0c178d6 100644
--- a/src/complex/add.mjs
+++ b/src/complex/add.mjs
@@ -7,16 +7,16 @@ export const add = {
     */
    'Complex,number': ({
       'self(number,number)': addNum,
-      'complex(any,any)': cplx
+      'complex(number,number)': cplx
    }) => (z,x) => cplx(addNum(z.re, x), z.im),
 
    'Complex,bigint': ({
       'self(bigint,bigint)': addBigInt,
-      'complex(any,any)': cplx
+      'complex(bigint,bigint)': cplx
    }) => (z,x) => cplx(addBigInt(z.re, x), z.im),
 
    'Complex,Complex': ({
       self,
-      'complex(any,any)': cplx
-   }) => (w,z) => cplx(self(w.re, z.re), self(w.im, z.im))
+      complex
+   }) => (w,z) => complex(self(w.re, z.re), self(w.im, z.im))
 }
diff --git a/src/complex/associate.mjs b/src/complex/associate.mjs
new file mode 100644
index 0000000..f3106b4
--- /dev/null
+++ b/src/complex/associate.mjs
@@ -0,0 +1,17 @@
+export * from './Types/Complex.mjs'
+
+/* Returns true if w is z multiplied by a complex unit */
+export const associate = {
+    'Complex,Complex': ({
+        'multiply(Complex,Complex)': times,
+        'equalTT(Complex,Complex)': eq,
+        zero,
+        one,
+        complex,
+        'negate(Complex)': neg
+    }) => (w,z) => {
+        if (eq(w,z) || eq(w,neg(z))) return true
+        const ti = times(z, complex(zero(z.re), one(z.im)))
+        return eq(w,ti) || eq(w,neg(ti))
+    }
+}
diff --git a/src/complex/complex.mjs b/src/complex/complex.mjs
index 58d3e2e..c34434c 100644
--- a/src/complex/complex.mjs
+++ b/src/complex/complex.mjs
@@ -9,7 +9,8 @@ export const complex = {
    'undefined': () => u => u,
    'undefined,any': () => (u, y) => u,
    'any,undefined': () => (x, u) => u,
-   'any,any': () => (x, y) => ({re: x, im: y}),
+   'undefined,undefined': () => (u, v) => u,
+   'T,T': () => (x, y) => ({re: x, im: y}),
    /* Take advantage of conversions in typed-function */
    Complex: () => z => z
 }
diff --git a/src/complex/equal.mjs b/src/complex/equalTT.mjs
similarity index 95%
rename from src/complex/equal.mjs
rename to src/complex/equalTT.mjs
index 4eca63f..43fe0d1 100644
--- a/src/complex/equal.mjs
+++ b/src/complex/equalTT.mjs
@@ -1,6 +1,6 @@
 export * from './Types/Complex.mjs'
 
-export const equal = {
+export const equalTT = {
    'Complex,number': ({
       'isZero(number)': isZ,
       'self(number,number)': eqNum
diff --git a/src/complex/gcd.mjs b/src/complex/gcd.mjs
index 84aa849..238d811 100644
--- a/src/complex/gcd.mjs
+++ b/src/complex/gcd.mjs
@@ -3,15 +3,18 @@ import * as Complex from './Types/Complex.mjs'
 import gcdType from '../generic/gcdType.mjs'
 
 const imps = {
-   gcdComplexRaw: gcdType('Complex'),
+   gcdGIRaw: gcdType('GaussianInteger'),
    gcd: { // Only return gcds with positive real part
-      'Complex, Complex': ({gcdComplexRaw, sign, one, negate}) => (z,m) => {
-         const raw = gcdComplexRaw(z, m)
-         if (sign(raw.re) === one(raw.re)) return raw
-         return negate(raw)
+      'GaussianInteger,GaussianInteger': ({
+         'gcdGIRaw(GaussianInteger,GaussianInteger)': gcdRaw,
+         'sign(bigint)': sgn,
+         'negate(GaussianInteger)': neg
+      }) => (z,m) => {
+         const raw = gcdRaw(z, m)
+         if (sgn(raw.re) === 1n) return raw
+         return neg(raw)
       }
    }
 }
 
 export const gcd = PocomathInstance.merge(Complex, imps)
-
diff --git a/src/complex/native.mjs b/src/complex/native.mjs
index 70d6b14..420ce88 100644
--- a/src/complex/native.mjs
+++ b/src/complex/native.mjs
@@ -1,13 +1,12 @@
-import gcdType from '../generic/gcdType.mjs'
-
 export * from './Types/Complex.mjs'
 
 export {abs} from './abs.mjs'
 export {absquare} from './absquare.mjs'
 export {add} from './add.mjs'
-export {conjugate} from './conjugate.mjs'
+export {associate} from './associate.mjs'
 export {complex} from './complex.mjs'
-export {equal} from './equal.mjs'
+export {conjugate} from './conjugate.mjs'
+export {equalTT} from './equalTT.mjs'
 export {gcd} from './gcd.mjs'
 export {invert} from './invert.mjs'
 export {isZero} from './isZero.mjs'
diff --git a/src/core/PocomathInstance.mjs b/src/core/PocomathInstance.mjs
index 6fab6c9..05636d4 100644
--- a/src/core/PocomathInstance.mjs
+++ b/src/core/PocomathInstance.mjs
@@ -1,12 +1,13 @@
 /* Core of pocomath: create an instance */
 import typed from 'typed-function'
-import dependencyExtractor from './dependencyExtractor.mjs'
+import {dependencyExtractor, generateTypeExtractor} from './extractors.mjs'
 import {makeChain} from './Chain.mjs'
-import {subsetOfKeys, typesOfSignature} from './utils.mjs'
+import {typeListOfSignature, typesOfSignature, subsetOfKeys} from './utils.mjs'
 
 const anySpec = {} // fixed dummy specification of 'any' type
 
 const theTemplateParam = 'T' // First pass: only allow this one exact parameter
+const templateFromParam = 'U' // For defining covariant conversions
 
 /* Returns a new signature just like sig but with the parameter replaced by
  * the type
@@ -27,7 +28,10 @@ export default class PocomathInstance {
       'importDependencies',
       'install',
       'installType',
+      'joinTypes',
       'name',
+      'self',
+      'Templates',
       'typeOf',
       'Types',
       'undefinedTypes'
@@ -39,11 +43,17 @@ export default class PocomathInstance {
       this._affects = {}
       this._typed = typed.create()
       this._typed.clear()
+      this._typed.addTypes([{name: 'ground', test: () => true}])
       /* List of types installed in the instance. We start with just dummies
        * for the 'any' type and for type parameters:
        */
       this.Types = {any: anySpec}
       this.Types[theTemplateParam] = anySpec
+      this.Types.ground = anySpec
+      // All the template types that have been defined
+      this.Templates = {}
+      // The actual type testing functions
+      this._typeTests = {}
       this._subtypes = {} // For each type, gives all of its (in)direct subtypes
       /* The following gives for each type, a set of all types that could
        * match in typed-function's dispatch algorithm before the given type.
@@ -52,8 +62,8 @@ export default class PocomathInstance {
        * might match.
        */
       this._priorTypes = {}
-      this._usedTypes = new Set() // all types that have occurred in a signature
-      this._doomed = new Set() // for detecting circular reference
+      this._seenTypes = new Set() // all types that have occurred in a signature
+      this._invalid = new Set() // methods that are currently invalid
       this._config = {predictable: false, epsilon: 1e-12}
       const self = this
       this.config = new Proxy(this._config, {
@@ -68,6 +78,12 @@ export default class PocomathInstance {
       })
       this._plainFunctions = new Set() // the names of the plain functions
       this._chainRepository = {} // place to store chainified functions
+
+      this._installFunctions({
+         typeOf: {ground: {uses: new Set(), does: () => () => 'any'}}
+      })
+
+      this.joinTypes = this.joinTypes.bind(this)
    }
 
    /**
@@ -177,9 +193,12 @@ export default class PocomathInstance {
 
    _installInstance(other) {
       for (const [type, spec] of Object.entries(other.Types)) {
-         if (type === 'any' || this._templateParam(type)) continue
+         if (spec === anySpec) continue
          this.installType(type, spec)
       }
+      for (const [base, info] of Object.entries(other.Templates)) {
+         this._installTemplateType(info.type, info.spec)
+      }
       const migrateImps = {}
       for (const operator in other._imps) {
          if (operator != 'typeOf') { // skip the builtin, we already have it
@@ -262,10 +281,15 @@ export default class PocomathInstance {
     * the corresponding changes to the _typed object immediately
     */
    installType(type, spec) {
-      if (this._templateParam(type)) {
+      const parts = type.split(/[<,>]/)
+      if (this._templateParam(parts[0])) {
          throw new SyntaxError(
             `Type name '${type}' reserved for template parameter`)
       }
+      if (parts.some(this._templateParam.bind(this))) {
+         // It's a template, deal with it separately
+         return this._installTemplateType(type, spec)
+      }
       if (type in this.Types) {
          if (spec !== this.Types[type]) {
             throw new SyntaxError(`Conflicting definitions of type ${type}`)
@@ -278,7 +302,7 @@ export default class PocomathInstance {
       }
       let beforeType = spec.refines
       if (!beforeType) {
-         beforeType = 'any'
+         beforeType = 'ground'
          for (const other of spec.before || []) {
             if (other in this.Types) {
                beforeType = other
@@ -291,68 +315,129 @@ export default class PocomathInstance {
          const supertypeTest = this.Types[spec.refines].test
          testFn = entity => supertypeTest(entity) && spec.test(entity)
       }
+      this._typeTests[type] = testFn
       this._typed.addTypes([{name: type, test: testFn}], beforeType)
       this.Types[type] = spec
+      this._subtypes[type] = new Set()
       this._priorTypes[type] = new Set()
+      // Update all the subtype sets of supertypes up the chain
+      let nextSuper = spec.refines
+      while (nextSuper) {
+         this._invalidateDependents(':' + nextSuper)
+         this._priorTypes[nextSuper].add(type)
+         this._subtypes[nextSuper].add(type)
+         nextSuper = this.Types[nextSuper].refines
+      }
       /* Now add conversions to this type */
       for (const from in (spec.from || {})) {
          if (from in this.Types) {
             // add conversions from "from" to this one and all its supertypes:
             let nextSuper = type
             while (nextSuper) {
+               if (this._priorTypes[nextSuper].has(from)) break
                this._typed.addConversion(
                   {from, to: nextSuper, convert: spec.from[from]})
                this._invalidateDependents(':' + nextSuper)
                this._priorTypes[nextSuper].add(from)
+               /* And all of the subtypes of from are now prior as well: */
+               for (const subtype of this._subtypes[from]) {
+                  this._priorTypes[nextSuper].add(subtype)
+               }
                nextSuper = this.Types[nextSuper].refines
             }
          }
       }
       /* And add conversions from this type */
       for (const to in this.Types) {
-         if (type in (this.Types[to].from || {})) {
-            if (spec.refines == to || spec.refines in this._subtypes[to]) {
-               throw new SyntaxError(
-                  `Conversion of ${type} to its supertype ${to} disallowed.`)
-            }
-            let nextSuper = to
-            while (nextSuper) {
-               this._typed.addConversion({
-                  from: type,
-                  to: nextSuper,
-                  convert: this.Types[to].from[type]
-               })
-               this._invalidateDependents(':' + nextSuper)
-               this._priorTypes[nextSuper].add(type)
-               nextSuper = this.Types[nextSuper].refines
+         for (const fromtype in this.Types[to].from) {
+            if (type == fromtype
+                || (fromtype in this._subtypes
+                    && this._subtypes[fromtype].has(type))) {
+               if (spec.refines == to || spec.refines in this._subtypes[to]) {
+                  throw new SyntaxError(
+                     `Conversion of ${type} to its supertype ${to} disallowed.`)
+               }
+               let nextSuper = to
+               while (nextSuper) {
+                  this._typed.addConversion({
+                     from: type,
+                     to: nextSuper,
+                     convert: this.Types[to].from[fromtype]
+                  })
+                  this._invalidateDependents(':' + nextSuper)
+                  this._priorTypes[nextSuper].add(type)
+                  nextSuper = this.Types[nextSuper].refines
+               }
             }
          }
       }
-      // Update all the subtype sets of supertypes up the chain, and
-      // while we are at it add trivial conversions from subtypes to supertypes
-      // to help typed-function match signatures properly:
-      this._subtypes[type] = new Set()
-      let nextSuper = spec.refines
-      while (nextSuper) {
-         this._typed.addConversion(
-            {from: type, to: nextSuper, convert: x => x})
-         this._invalidateDependents(':' + nextSuper)
-         this._priorTypes[nextSuper].add(type)
-         this._subtypes[nextSuper].add(type)
-         nextSuper = this.Types[nextSuper].refines
-      }
-
       // update the typeOf function
       const imp = {}
       imp[type] = {uses: new Set(), does: () => () => type}
       this._installFunctions({typeOf: imp})
    }
 
+   /* Returns the most refined type of all the types in the array, with
+    * '' standing for the empty type for convenience. If the second
+    * argument `convert` is true, a convertible type is considered a
+    * a subtype (defaults to false).
+    */
+   joinTypes(types, convert) {
+      let join = ''
+      for (const type of types) {
+         join = this._joinTypes(join, type, convert)
+      }
+      return join
+   }
+   /* helper for above */
+   _joinTypes(typeA, typeB, convert) {
+      if (!typeA) return typeB
+      if (!typeB) return typeA
+      if (typeA === 'any' || typeB === 'any') return 'any'
+      if (typeA === 'ground' || typeB === 'ground') return 'ground'
+      if (typeA === typeB) return typeA
+      const subber = convert ? this._priorTypes : this._subtypes
+      if (subber[typeB].has(typeA)) return typeB
+      /* OK, so we need the most refined supertype of A that contains B:
+       */
+      let nextSuper = typeA
+      while (nextSuper) {
+         if (subber[nextSuper].has(typeB)) return nextSuper
+         nextSuper = this.Types[nextSuper].refines
+      }
+      /* And if conversions are allowed, we have to search the other way too */
+      if (convert) {
+         nextSuper = typeB
+         while (nextSuper) {
+            if (subber[nextSuper].has(typeA)) return nextSuper
+            nextSuper = this.Types[nextSuper].refines
+         }
+      }
+      return 'any'
+   }
+
    /* Returns a list of all types that have been mentioned in the
     * signatures of operations, but which have not actually been installed:
     */
    undefinedTypes() {
-      return Array.from(this._usedTypes).filter(t => !(t in this.Types))
+      return Array.from(this._seenTypes).filter(t => !(t in this.Types))
+   }
+
+   /* Used internally to install a template type */
+   _installTemplateType(type, spec) {
+      const base = type.split('<')[0]
+      /* For now, just allow a single template per base type; that
+       * might need to change later:
+       */
+      if (base in this.Templates) {
+         if (spec !== this.Templates[base].spec) {
+            throw new SyntaxError(
+               `Conflicting definitions of template type ${type}`)
+         }
+         return
+      }
+      // Nothing actually happens until we match a template parameter
+      this.Templates[base] = {type, spec}
    }
 
    /* Used internally by install, see the documentation there */
@@ -392,9 +477,12 @@ export default class PocomathInstance {
                   this._addAffect(depname, name)
                }
                for (const type of typesOfSignature(signature)) {
-                  if (this._templateParam(type)) continue
-                  this._usedTypes.add(type)
-                  this._addAffect(':' + type, name)
+                  for (const word of type.split(/[<>]/)) {
+                     if (word.length == 0) continue
+                     if (this._templateParam(word)) continue
+                     this._seenTypes.add(word)
+                     this._addAffect(':' + word, name)
+                  }
                }
             }
          }
@@ -420,20 +508,20 @@ export default class PocomathInstance {
     * and if it has no implementations so far, set them up.
     */
    _invalidate(name) {
-      if (this._doomed.has(name)) {
-         /* In the midst of a circular invalidation, so do nothing */
-         return
-      }
+      if (this._invalid.has(name)) return
       if (!(name in this._imps)) {
          this._imps[name] = {}
       }
-      this._doomed.add(name)
+      this._invalid.add(name)
       this._invalidateDependents(name)
-      this._doomed.delete(name)
       const self = this
       Object.defineProperty(this, name, {
          configurable: true,
-         get: () => self._bundle(name)
+         get: () => {
+            const result = self._bundle(name)
+            self._invalid.delete(name)
+            return result
+         }
       })
    }
 
@@ -457,22 +545,38 @@ export default class PocomathInstance {
       if (!imps) {
          throw new SyntaxError(`No implementations for ${name}`)
       }
-      const usableEntries = Object.entries(imps).filter(
-         ([signature]) => subsetOfKeys(typesOfSignature(signature), this.Types))
+      /* Collect the entries we know the types for */
+      const usableEntries = []
+      for (const entry of Object.entries(imps)) {
+         let keep = true
+         for (const type of typesOfSignature(entry[0])) {
+            if (type in this.Types) continue
+            const baseType = type.split('<')[0]
+            if (baseType in this.Templates) continue
+            keep = false
+            break
+         }
+         if (keep) usableEntries.push(entry)
+      }
       if (usableEntries.length === 0) {
          throw new SyntaxError(
             `Every implementation for ${name} uses an undefined type;\n`
                + `    signatures: ${Object.keys(imps)}`)
       }
+      /* Initial error checking done; mark this method as being
+       * in the midst of being reassembled
+       */
       Object.defineProperty(this, name, {configurable: true, value: 'limbo'})
       const tf_imps = {}
       for (const [rawSignature, behavior] of usableEntries) {
          /* Check if it's an ordinary non-template signature */
          let explicit = true
          for (const type of typesOfSignature(rawSignature)) {
-            if (this._templateParam(type)) { // template types need better check
-               explicit = false
-               break
+            for (const word of type.split(/[<>]/)) {
+               if (this._templateParam(word)) {
+                  explicit = false
+                  break
+               }
             }
          }
          if (explicit) {
@@ -485,16 +589,10 @@ export default class PocomathInstance {
             behavior.instantiations = new Set()
          }
          let instantiationSet = new Set()
-         let trimSignature = rawSignature
-         if (rawSignature.charAt(0) === '!') {
-            trimSignature = trimSignature.slice(1)
-            instantiationSet = this._usedTypes
-         } else {
-            for (const instType of behavior.instantiations) {
-               instantiationSet.add(instType)
-               for (const other of this._priorTypes[instType]) {
-                  instantiationSet.add(other)
-               }
+         for (const instType of behavior.instantiations) {
+            instantiationSet.add(instType)
+            for (const other of this._priorTypes[instType]) {
+               instantiationSet.add(other)
             }
          }
 
@@ -502,7 +600,7 @@ export default class PocomathInstance {
             if (!(instType in this.Types)) continue
             if (this.Types[instType] === anySpec) continue
             const signature =
-                  substituteInSig(trimSignature, theTemplateParam, instType)
+                  substituteInSig(rawSignature, theTemplateParam, instType)
             /* Don't override an explicit implementation: */
             if (signature in imps) continue
             const uses = new Set()
@@ -521,44 +619,170 @@ export default class PocomathInstance {
                      innerRefs[dep] = refs[outerName]
                   }
                }
-               const original = behavior.does(innerRefs)
                return behavior.does(innerRefs)
             }
-            this._addTFimplementation(tf_imps, signature, {uses, does: patch})
+            this._addTFimplementation(
+               tf_imps, signature, {uses, does: patch})
          }
          /* Now add the catchall signature */
+         let templateCall = `<${theTemplateParam}>`
+         /* Relying here that the base of 'Foo<T>' is 'Foo': */
+         let baseSignature = rawSignature.replaceAll(templateCall, '')
+         /* Any remaining template params are top-level */
          const signature = substituteInSig(
-            trimSignature, theTemplateParam, 'any')
+            baseSignature, theTemplateParam, 'ground')
          /* The catchall signature has to detect the actual type of the call
-          * and add the new instantiations
+          * and add the new instantiations.
+          * First, prepare the type inference data:
           */
-         const argTypes = trimSignature.split(',')
-         let exemplar = -1
-         for (let i = 0; i < argTypes.length; ++i) {
-            const argType = argTypes[i].trim()
-            if (argType === theTemplateParam) {
-               exemplar = i
-               break
-            }
-         }
-         if (exemplar < 0) {
+         const parTypes = rawSignature.split(',')
+         const restParam = (parTypes[parTypes.length-1].slice(0,3) === '...')
+         const topTyper = entity => this.typeOf(entity)
+         const inferences = parTypes.map(
+            type => generateTypeExtractor(
+               type,
+               theTemplateParam,
+               topTyper,
+               this.joinTypes.bind(this),
+               this.Templates))
+         if (inferences.every(x => !x)) { // all false
             throw new SyntaxError(
                `Cannot find template parameter in ${rawSignature}`)
          }
+         /* And eliminate template parameters from the dependencies */
+         const simplifiedUses = {}
+         for (const dep of behavior.uses) {
+            let [func, needsig] = dep.split(/[()]/)
+            if (needsig) {
+               const subsig = substituteInSig(needsig, theTemplateParam, '')
+               if (subsig === needsig) {
+                  simplifiedUses[dep] = dep
+               } else {
+                  simplifiedUses[dep] = func
+               }
+            } else {
+               simplifiedUses[dep] = dep
+            }
+         }
+         /* Now build the catchall implementation */
          const self = this
          const patch = (refs) => (...args) => {
-            const example = args[exemplar]
-            const instantiateFor = self.typeOf(example)
+            /* We unbundle the rest arg if there is one */
+            const regLength = args.length - 1
+            if (restParam) {
+               const restArgs = args.pop()
+               args = args.concat(restArgs)
+            }
+            /* Now infer the type we actually should have been called for */
+            let i = -1
+            let j = -1
+            /* collect the arg types */
+            const argTypes = []
+            for (const arg of args) {
+               ++j
+               // in case of rest parameter, reuse last parameter type:
+               if (i < inferences.length - 1) ++i
+               if (inferences[i]) {
+                  const argType = inferences[i](arg)
+                  if (!argType) {
+                     throw TypeError(
+                        `Type inference failed for argument ${j} of ${name}`)
+                  }
+                  if (argType === 'any') {
+                     throw TypeError(
+                        `In call to ${name}, incompatible template arguments: `
+                           + args.map(a => JSON.stringify(a)).join(', '))
+                  }
+                  argTypes.push(argType)
+               }
+            }
+            if (argTypes.length === 0) {
+               throw TypeError('Type inference failed for' + name)
+            }
+            let usedConversions = false
+            let instantiateFor = self.joinTypes(argTypes)
+            if (instantiateFor === 'any') {
+               usedConversions = true
+               instantiateFor = self.joinTypes(argTypes, usedConversions)
+               if (instantiateFor === 'any') {
+                  throw TypeError(
+                     `In call to ${name}, no type unifies arguments `
+                        + args.toString() + '; of types ' + argTypes.toString()
+                        + '; note each consecutive pair must unify to a '
+                        + 'supertype of at least one of them')
+               }
+            }
+            /* Generate the list of actual wanted types */
+            const wantTypes = parTypes.map(type => substituteInSig(
+               type, theTemplateParam, instantiateFor))
+            /* Now we have to add any actual types that are relevant
+             * to this invocation. Namely, that would be every formal parameter
+             * type in the invocation, with the parameter template instantiated
+             * by instantiateFor, and for all of instantiateFor's "prior types"
+             */
+            for (j = 0; j < parTypes.length; ++j) {
+               if (wantTypes[j] !== parTypes[j] && parTypes[j].includes('<')) {
+                  // actually used the param and is a template
+                  self._ensureTemplateTypes(parTypes[j], instantiateFor)
+               }
+            }
+            /* Transform the arguments if we used any conversions: */
+            if (usedConversions) {
+               i = - 1
+               for (j = 0; j < args.length; ++j) {
+                  if (i < parTypes.length - 1) ++i
+                  let wantType = parTypes[i]
+                  if (wantType.slice(0,3) === '...') {
+                     wantType = wantType.slice(3)
+                  }
+                  wantType = substituteInSig(
+                     wantType, theTemplateParam, instantiateFor)
+                  if (wantType !== parTypes[i]) {
+                     args[j] = self._typed.convert(args[j], wantType)
+                  }
+               }
+            }
+            /* Finally reassemble the rest args if there were any */
+            if (restParam) {
+               const restArgs = args.slice(regLength)
+               args = args.slice(0,regLength)
+               args.push(restArgs)
+            }
+            /* Arrange that the desired instantiation will be there next
+             * time so we don't have to go through that again for this type
+             */
             refs[theTemplateParam] = instantiateFor
             behavior.instantiations.add(instantiateFor)
             self._invalidate(name)
-            // And for now, we have to rely on the "any" implementation. Hope
-            // it matches the instantiated one!
-            return behavior.does(refs)(...args)
+            // And update refs because we now know the type we're instantiating
+            // for:
+            const innerRefs = {}
+            for (const dep in simplifiedUses) {
+               const simplifiedDep = simplifiedUses[dep]
+               if (dep === simplifiedDep) {
+                  innerRefs[dep] = refs[dep]
+               } else {
+                  let [func, needsig] = dep.split(/[()]/)
+                  if (self._typed.isTypedFunction(refs[simplifiedDep])) {
+                     const subsig = substituteInSig(
+                        needsig, theTemplateParam, instantiateFor)
+                     let resname = simplifiedDep
+                     if (resname === 'self') resname = name
+                     innerRefs[dep] = self._pocoresolve(resname, subsig)
+                  } else {
+                     innerRefs[dep] = refs[simplifiedDep]
+                  }
+               }
+            }
+            // Finally ready to make the call.
+            return behavior.does(innerRefs)(...args)
          }
+         // The actual uses value needs to be a set:
+         const outerUses = new Set(Object.values(simplifiedUses))
          this._addTFimplementation(
-            tf_imps, signature, {uses: behavior.uses, does: patch})
+            tf_imps, signature, {uses: outerUses, does: patch})
       }
+      this._correctPartialSelfRefs(tf_imps)
       const tf = this._typed(name, tf_imps)
       Object.defineProperty(this, name, {configurable: true, value: tf})
       return tf
@@ -579,9 +803,17 @@ export default class PocomathInstance {
       let part_self_references = []
       for (const dep of uses) {
          let [func, needsig] = dep.split(/[()]/)
-         const needTypes = needsig ? typesOfSignature(needsig) : new Set()
-         /* For now, punt on template parameters */
-         if (needTypes.has(theTemplateParam)) needsig = ''
+         /* Safety check that can perhaps be removed:
+          * Verify that the desired signature has been fully grounded:
+          */
+         if (needsig) {
+            const trysig = substituteInSig(needsig, theTemplateParam, '')
+            if (trysig !== needsig) {
+               throw new Error(
+                  'Attempt to add a template implementation: ' +
+                     `${signature} with dependency ${dep}`)
+            }
+         }
          if (func === 'self') {
             if (needsig) {
                if (full_self_referential) {
@@ -614,7 +846,7 @@ export default class PocomathInstance {
                // can bundle up func, and grab its signature if need be
                let destination = this[func]
                if (needsig) {
-                  destination = this._typed.find(destination, needsig)
+                  destination = this._pocoresolve(func, needsig)
                }
                refs[dep] = destination
             }
@@ -628,16 +860,215 @@ export default class PocomathInstance {
          return
       }
       if (part_self_references.length) {
-         imps[signature] = this._typed.referTo(
-            ...part_self_references, (...impls) => {
+         /* There is an obstruction here. The list part_self_references
+          * might contain a signature that requires conversion for self to
+          * handle. But I advocated this not be allowed in typed.referTo, which
+          * made sense for human-written functions, but is unfortunate now.
+          * So we have to defer creating these and correct them later, at
+          * least until we can add an option to typed-function.
+          */
+         imps[signature] = {
+            deferred: true,
+            builtRefs: refs,
+            sigDoes: does,
+            psr: part_self_references
+         }
+         return
+      }
+      imps[signature] = does(refs)
+   }
+
+   _correctPartialSelfRefs(imps) {
+      for (const aSignature in imps) {
+         if (!(imps[aSignature].deferred)) continue
+         const part_self_references = imps[aSignature].psr
+         const corrected_self_references = []
+         for (const neededSig of part_self_references) {
+            // Have to find a match for neededSig among the other signatures
+            // of this function. That's a job for typed-function, but we will
+            // try here:
+            if (neededSig in imps) { // the easy case
+               corrected_self_references.push(neededSig)
+               continue
+            }
+            // No exact match, try to get one that matches with
+            // subtypes since the whole conversion thing in typed-function
+            // is too complicated to reproduce
+            const foundSig = this._findSubtypeImpl(imps, neededSig)
+            if (foundSig) {
+               corrected_self_references.push(foundSig)
+            } else {
+               throw new Error(
+                  'Implement inexact self-reference in typed-function for '
+                     + neededSig)
+            }
+         }
+         const refs = imps[aSignature].builtRefs
+         const does = imps[aSignature].sigDoes
+         imps[aSignature] = this._typed.referTo(
+            ...corrected_self_references, (...impls) => {
                for (let i = 0; i < part_self_references.length; ++i) {
                   refs[`self(${part_self_references[i]})`] = impls[i]
                }
                return does(refs)
             }
          )
-         return
       }
-      imps[signature] = does(refs)
    }
+
+   /* This function analyzes the template and makes sure the
+    * instantiations of it for type and all prior types of type are present
+    * in the instance.
+    */
+   _ensureTemplateTypes(template, type) {
+      let [base, arg] = template.split('<', 2)
+      arg = arg.slice(0,-1)
+      if (!arg) {
+         throw new Error(
+            'Implementation error in _ensureTemplateTypes', template, type)
+      }
+      let instantiations
+      if (this._templateParam(arg)) { // 1st-level template
+         instantiations = new Set(this._priorTypes[type])
+         instantiations.add(type)
+      } else { // nested template
+         instantiations = this._ensureTemplateTypes(arg, type)
+      }
+      const resultingTypes = new Set()
+      for (const iType of instantiations) {
+         const resultType = this._maybeAddTemplateType(base, iType)
+         if (resultType) resultingTypes.add(resultType)
+      }
+      return resultingTypes
+   }
+
+   /* Maybe add the instantiation of template type base with argument tyoe
+    * instantiator to the Types of this instance, if it hasn't happened already.
+    * Returns the name of the type if added, false otherwise.
+    */
+   _maybeAddTemplateType(base, instantiator) {
+      const wantsType = `${base}<${instantiator}>`
+      if (wantsType in this.Types) return false
+      // OK, need to generate the type from the template
+      // Set up refines, before, test, and from
+      const newTypeSpec = {refines: base}
+      const maybeFrom = {}
+      const template = this.Templates[base].spec
+      if (!template) {
+         throw new Error(
+            `Implementor error in _maybeAddTemplateType ${base} ${instantiator}`)
+      }
+      const instantiatorSpec = this.Types[instantiator]
+      let beforeTypes = []
+      if (instantiatorSpec.before) {
+         beforeTypes = instantiatorSpec.before.map(type => `${base}<${type}>`)
+      }
+      if (template.before) {
+         for (const beforeTmpl of template.before) {
+            beforeTypes.push(
+               substituteInSig(beforeTmpl, theTemplateParam, instantiator))
+         }
+      }
+      if (beforeTypes.length > 0) {
+         newTypeSpec.before = beforeTypes
+      }
+      newTypeSpec.test = template.test(this._typeTests[instantiator])
+      if (template.from) {
+         for (let source in template.from) {
+            const instSource = substituteInSig(
+               source, theTemplateParam, instantiator)
+            let usesFromParam = false
+            for (const word of instSource.split(/[<>]/)) {
+               if (word === templateFromParam) {
+                  usesFromParam = true
+                  break
+               }
+            }
+            if (usesFromParam) {
+               for (const iFrom in instantiatorSpec.from) {
+                  const finalSource = substituteInSig(
+                     instSource, templateFromParam, iFrom)
+                  maybeFrom[finalSource] = template.from[source](
+                     instantiatorSpec.from[iFrom])
+               }
+               // Assuming all templates are covariant here, I guess...
+               for (const subType of this._subtypes[instantiator]) {
+                  const finalSource = substituteInSig(
+                     instSource, templateFromParam, subType)
+                  maybeFrom[finalSource] = template.from[source](x => x)
+               }
+            } else {
+               maybeFrom[instSource] = template.from[source]
+            }
+         }
+      }
+
+      if (Object.keys(maybeFrom).length > 0) {
+         newTypeSpec.from = maybeFrom
+      }
+      this.installType(wantsType, newTypeSpec)
+      return wantsType
+   }
+
+   _findSubtypeImpl(imps, neededSig) {
+      if (neededSig in imps) return neededSig
+      let foundSig = false
+      const typeList = typeListOfSignature(neededSig)
+      for (const otherSig in imps) {
+         const otherTypeList = typeListOfSignature(otherSig)
+         if (typeList.length !== otherTypeList.length) continue
+         let allMatch = true
+         for (let k = 0; k < typeList.length; ++k) {
+            let myType = typeList[k]
+            let otherType = otherTypeList[k]
+            if (otherType === theTemplateParam) {
+               otherTypeList[k] = 'ground'
+               otherType = 'ground'
+            }
+            if (otherType === '...T') {
+               otherTypeList[k] = '...ground'
+               otherType = 'ground'
+            }
+            const adjustedOtherType = otherType.replaceAll(
+               `<${theTemplateParam}>`, '')
+            if (adjustedOtherType !== otherType) {
+               otherTypeList[k] = adjustedOtherType
+               otherType = adjustedOtherType
+            }
+            if (myType.slice(0,3) === '...') myType = myType.slice(3)
+            if (otherType.slice(0,3) === '...') otherType = otherType.slice(3)
+            if (otherType === 'any') continue
+            if (otherType === 'ground') continue
+            if (!(otherType in this.Types)) {
+               allMatch = false
+               break
+            }
+            if (myType === otherType
+                || this._subtypes[otherType].has(myType)) {
+               continue
+            }
+            allMatch = false
+            break
+         }
+         if (allMatch) {
+            foundSig = otherTypeList.join(',')
+            break
+         }
+      }
+      return foundSig
+   }
+
+   _pocoresolve(name, sig) {
+      const typedfunc = this[name]
+      let result = undefined
+      try {
+         result = this._typed.find(typedfunc, sig, {exact: true})
+      } catch {
+      }
+      if (result) return result
+      const foundsig = this._findSubtypeImpl(this._imps[name], sig)
+      if (foundsig) return this._typed.find(typedfunc, foundsig)
+      return this._typed.find(typedfunc, sig)
+   }
+
 }
diff --git a/src/core/dependencyExtractor.mjs b/src/core/dependencyExtractor.mjs
deleted file mode 100644
index 1b1091c..0000000
--- a/src/core/dependencyExtractor.mjs
+++ /dev/null
@@ -1,12 +0,0 @@
-/* Call this with an empty Set object S, and it returns an entity E
- * from which properties can be extracted, and at any time S will
- * contain all of the property names that have been extracted from E.
- */
-export default function dependencyExtractor(destinationSet) {
-   return new Proxy({}, {
-      get: (target, property) => {
-         destinationSet.add(property)
-         return {}
-      }
-   })
-}
diff --git a/src/core/extractors.mjs b/src/core/extractors.mjs
new file mode 100644
index 0000000..0db3c0f
--- /dev/null
+++ b/src/core/extractors.mjs
@@ -0,0 +1,41 @@
+/* Call this with an empty Set object S, and it returns an entity E
+ * from which properties can be extracted, and at any time S will
+ * contain all of the property names that have been extracted from E.
+ */
+export function dependencyExtractor(destinationSet) {
+   return new Proxy({}, {
+      get: (target, property) => {
+         destinationSet.add(property)
+         return {}
+      }
+   })
+}
+
+/* Given a (template) type name, what the template parameter is,
+ * a top level typer, and a library of templates,
+ * produces a function that will extract the instantantion type from an
+ * instance. Currently relies heavily on there being only unary templates.
+ *
+ * We should really be using the typed-function parser to do the
+ * manipulations below, but at the moment we don't have access.
+ */
+export function generateTypeExtractor(
+   type, param, topTyper, typeJoiner, templates)
+{
+   type = type.trim()
+   if (type.slice(0,3) === '...') {
+      type = type.slice(3).trim()
+   }
+   if (type === param) return topTyper
+   if (!(type.includes('<'))) return false // no template type to extract
+   const base = type.split('<',1)[0]
+   if (!(base in templates)) return false // unknown template
+   const arg = type.slice(base.length+1, -1)
+   const argExtractor = generateTypeExtractor(
+      arg, param, topTyper, typeJoiner, templates)
+   if (!argExtractor) return false
+   return templates[base].spec.infer({
+      typeOf: argExtractor,
+      joinTypes: typeJoiner
+   })
+}
diff --git a/src/core/utils.mjs b/src/core/utils.mjs
index 11a879f..db164dd 100644
--- a/src/core/utils.mjs
+++ b/src/core/utils.mjs
@@ -6,6 +6,11 @@ export function subsetOfKeys(set, obj) {
    return true
 }
 
+/* Returns a list of the types mentioned in a typed-function signature */
+export function typeListOfSignature(signature) {
+   return signature.split(',').map(s => s.trim())
+}
+
 /* Returns a set of all of the types mentioned in a typed-function signature */
 export function typesOfSignature(signature) {
    return new Set(signature.split(/[^\w\d]/).filter(s => s.length))
diff --git a/src/generic/arithmetic.mjs b/src/generic/arithmetic.mjs
index f6abd23..00faddb 100644
--- a/src/generic/arithmetic.mjs
+++ b/src/generic/arithmetic.mjs
@@ -3,6 +3,8 @@ import {reducingOperation} from './reducingOperation.mjs'
 export * from './Types/generic.mjs'
 
 export const add = reducingOperation
+export const gcd = reducingOperation
+export {identity} from './identity.mjs'
 export {lcm} from './lcm.mjs'
 export {mean} from './mean.mjs'
 export {mod} from './mod.mjs'
diff --git a/src/generic/identity.mjs b/src/generic/identity.mjs
new file mode 100644
index 0000000..2422d2f
--- /dev/null
+++ b/src/generic/identity.mjs
@@ -0,0 +1,3 @@
+export function identity(x) {
+   return x
+}
diff --git a/src/generic/lcm.mjs b/src/generic/lcm.mjs
index adc3dfb..04e78b5 100644
--- a/src/generic/lcm.mjs
+++ b/src/generic/lcm.mjs
@@ -1,3 +1,5 @@
+import {reducingOperation} from './reducingOperation.mjs'
+
 export const lcm = {
    'T,T': ({
       'multiply(T,T)': multT,
@@ -5,3 +7,4 @@ export const lcm = {
       'gcd(T,T)': gcdT
    }) => (a,b) => multT(quotT(a, gcdT(a,b)), b)
 }
+Object.assign(lcm, reducingOperation)
diff --git a/src/generic/relational.mjs b/src/generic/relational.mjs
index 368f394..939ae19 100644
--- a/src/generic/relational.mjs
+++ b/src/generic/relational.mjs
@@ -7,14 +7,27 @@ export const isZero = {
 }
 
 export const equal = {
-   '!T,T': ({
+   'any,any': ({equalTT, joinTypes, Templates, typeOf}) => (x,y) => {
+      const resultant = joinTypes([typeOf(x), typeOf(y)], 'convert')
+      if (resultant === 'any' || resultant in Templates) {
+         return false
+      }
+      return equalTT(x,y)
+   }
+}
+
+export const equalTT = {
+   'T,T': ({
       'compare(T,T)': cmp,
       'isZero(T)': isZ
-   }) => (x,y) => isZ(cmp(x,y))
+   }) => (x,y) => isZ(cmp(x,y)),
+   // If templates were native to typed-function, we should be able to
+   // do something like:
+   // 'any,any': () => () => false // should only be hit for different types
 }
 
 export const unequal = {
-   'T,T': ({'equal(T.T)': eq}) => (x,y) => !(eq(x,y))
+   'any,any': ({equal}) => (x,y) => !(equal(x,y))
 }
 
 export const larger = {
diff --git a/src/number/native.mjs b/src/number/native.mjs
index 1404ab4..d095574 100644
--- a/src/number/native.mjs
+++ b/src/number/native.mjs
@@ -1,10 +1,12 @@
 import gcdType from '../generic/gcdType.mjs'
+import {identity} from '../generic/identity.mjs'
 
 export * from './Types/number.mjs'
 
 export {abs} from './abs.mjs'
 export {add} from './add.mjs'
 export {compare} from './compare.mjs'
+export const conjugate = {number: () => identity}
 export const gcd = gcdType('NumInt')
 export {invert} from './invert.mjs'
 export {isZero} from './isZero.mjs'
diff --git a/src/ops/floor.mjs b/src/ops/floor.mjs
index 98d524a..e8897e8 100644
--- a/src/ops/floor.mjs
+++ b/src/ops/floor.mjs
@@ -12,7 +12,7 @@ export const floor = {
    // entry with type `bigint|NumInt|GaussianInteger` because they couldn't
    // be separately activated then
 
-   number: ({'equal(number,number)': eq}) => n => {
+   number: ({'equalTT(number,number)': eq}) => n => {
       if (eq(n, Math.round(n))) return Math.round(n)
       return Math.floor(n)
    },
diff --git a/src/pocomath.mjs b/src/pocomath.mjs
index dee980e..d8df045 100644
--- a/src/pocomath.mjs
+++ b/src/pocomath.mjs
@@ -3,10 +3,11 @@ import PocomathInstance from './core/PocomathInstance.mjs'
 import * as numbers from './number/native.mjs'
 import * as bigints from './bigint/native.mjs'
 import * as complex from './complex/native.mjs'
+import * as tuple from './tuple/native.mjs'
 import * as generic from './generic/all.mjs'
 import * as ops from './ops/all.mjs'
 
 const math = PocomathInstance.merge(
-    'math', numbers, bigints, complex, generic, ops)
+    'math', numbers, bigints, complex, tuple, generic, ops)
 
 export default math
diff --git a/src/tuple/Types/Tuple.mjs b/src/tuple/Types/Tuple.mjs
new file mode 100644
index 0000000..0c6c0ae
--- /dev/null
+++ b/src/tuple/Types/Tuple.mjs
@@ -0,0 +1,80 @@
+/* A template type representing a homeogeneous tuple of elements */
+import PocomathInstance from '../../core/PocomathInstance.mjs'
+
+const Tuple = new PocomathInstance('Tuple')
+// First a base type that will generally not be used directly
+Tuple.installType('Tuple', {
+   test: t => t && typeof t === 'object' && 'elts' in t && Array.isArray(t.elts)
+})
+// Now the template type that is the primary use of this
+Tuple.installType('Tuple<T>', {
+   // We are assuming that any 'Type<T>' refines 'Type', so this is
+   // not necessary:
+   // refines: 'Tuple',
+   // But we need there to be a way to determine the type of a tuple:
+   infer: ({typeOf, joinTypes}) => t => joinTypes(t.elts.map(typeOf)),
+   // For the test, we can assume that t is already a base tuple,
+   // and we get the test for T as an input and we have to return
+   // the test for Tuple<T>
+   test: testT => t => t.elts.every(testT),
+   // These are only invoked for types U such that there is already
+   // a conversion from U to T, and that conversion is passed as an input
+   // and we have to return the conversion to Tuple<T>:
+   from: {
+      'Tuple<U>': convert => tu => ({elts: tu.elts.map(convert)}),
+      // Here since there is no U it's a straight conversion:
+      T: t => ({elts: [t]}), // singleton promotion
+      // Whereas the following will let you go directly from an element
+      // convertible to T to a singleton Tuple<T>. Not sure if we really
+      // want that, but we'll try it just for kicks.
+      U: convert => u => ({elts: [convert(u)]})
+   }
+})
+
+Tuple.promoteUnary = {
+   'Tuple<T>': ({'self(T)': me, tuple}) => t => tuple(...(t.elts.map(me)))
+}
+
+Tuple.promoteBinaryUnary = {
+   'Tuple<T>,Tuple<T>': ({'self(T,T)': meB, 'self(T)': meU, tuple}) => (s,t) => {
+      let i = -1
+      let result = []
+      while (true) {
+         i += 1
+         if (i < s.elts.length) {
+            if (i < t.elts.length) result.push(meB(s.elts[i], t.elts[i]))
+            else result.push(meU(s.elts[i]))
+            continue
+         }
+         if (i < t.elts.length) result.push(meU(t.elts[i]))
+         else break
+      }
+      return tuple(...result)
+   }
+}
+
+Tuple.promoteBinary = {
+   'Tuple<T>,Tuple<T>': ({'self(T,T)': meB, tuple}) => (s,t) => {
+      const lim = Math.max(s.elts.length, t.elts.length)
+      const result = []
+      for (let i = 0; i < lim; ++i) {
+         result.push(meB(s.elts[i], t.elts[i]))
+      }
+      return tuple(...result)
+   }
+}
+
+Tuple.promoteBinaryStrict = {
+   'Tuple<T>,Tuple<T>': ({'self(T,T)': meB, tuple}) => (s,t) => {
+      if (s.elts.length !== t.elts.length) {
+         throw new RangeError('Tuple length mismatch') // get name of self ??
+      }
+      const result = []
+      for (let i = 0; i < s.elts.length; ++i) {
+         result.push(meB(s.elts[i], t.elts[i]))
+      }
+      return tuple(...result)
+   }
+}
+
+export {Tuple}
diff --git a/src/tuple/equalTT.mjs b/src/tuple/equalTT.mjs
new file mode 100644
index 0000000..1606410
--- /dev/null
+++ b/src/tuple/equalTT.mjs
@@ -0,0 +1,11 @@
+export * from './Types/Tuple.mjs'
+
+export const equalTT = {
+   'Tuple<T>,Tuple<T>': ({'self(T,T)': me, 'length(Tuple)': len}) => (s,t) => {
+      if (len(s) !== len(t)) return false
+      for (let i = 0; i < len(s); ++i) {
+         if (!me(s.elts[i], t.elts[i])) return false
+      }
+      return true
+   }
+}
diff --git a/src/tuple/isZero.mjs b/src/tuple/isZero.mjs
new file mode 100644
index 0000000..9375277
--- /dev/null
+++ b/src/tuple/isZero.mjs
@@ -0,0 +1,8 @@
+export {Tuple} from './Types/Tuple.mjs'
+
+export const isZero = {
+   'Tuple<T>': ({'self(T)': me}) => t => t.elts.every(e => me(e))
+   // Note we can't just say `every(me)` above since every invokes its
+   // callback with more arguments, which then violates typed-function's
+   // signature for `me`
+}
diff --git a/src/tuple/length.mjs b/src/tuple/length.mjs
new file mode 100644
index 0000000..f3e8f2d
--- /dev/null
+++ b/src/tuple/length.mjs
@@ -0,0 +1,3 @@
+export {Tuple} from './Types/Tuple.mjs'
+
+export const length = {Tuple: () => t => t.elts.length}
diff --git a/src/tuple/native.mjs b/src/tuple/native.mjs
new file mode 100644
index 0000000..66ba8f0
--- /dev/null
+++ b/src/tuple/native.mjs
@@ -0,0 +1,21 @@
+import {Tuple} from './Types/Tuple.mjs'
+
+export const add = Tuple.promoteBinaryUnary
+export const complex = Tuple.promoteBinaryStrict
+export const conjugate = Tuple.promoteUnary
+export const divide = Tuple.promoteBinaryStrict
+export {equalTT} from './equalTT.mjs'
+export const invert = Tuple.promoteUnary
+export {isZero} from './isZero.mjs'
+export {length} from './length.mjs'
+export const multiply = Tuple.promoteBinaryUnary
+export const negate = Tuple.promoteUnary
+export const one = Tuple.promoteUnary
+export const quotient = Tuple.promoteBinaryStrict
+export const roundquotient = Tuple.promoteBinaryStrict
+export const sqrt = Tuple.promoteUnary
+export const subtract = Tuple.promoteBinaryStrict
+export {tuple} from './tuple.mjs'
+export const zero = Tuple.promoteUnary
+
+export {Tuple}
diff --git a/src/tuple/tuple.mjs b/src/tuple/tuple.mjs
new file mode 100644
index 0000000..893b54d
--- /dev/null
+++ b/src/tuple/tuple.mjs
@@ -0,0 +1,6 @@
+export {Tuple} from './Types/Tuple.mjs'
+
+/* The purpose of the template argument is to ensure that all of the args
+ * are convertible to the same type.
+ */
+export const tuple = {'...T': () => args => ({elts: args})}
diff --git a/test/_pocomath.mjs b/test/_pocomath.mjs
index 18643b0..1d7d1e9 100644
--- a/test/_pocomath.mjs
+++ b/test/_pocomath.mjs
@@ -103,4 +103,13 @@ describe('The default full pocomath instance "math"', () => {
       assert.strictEqual(math.choose(21n, 2n), 210n)
    })
 
+   it('calculates multi-way gcds and lcms', () => {
+      assert.strictEqual(math.gcd(30,105,42), 3)
+      assert.ok(
+         math.associate(
+            math.lcm(
+               math.complex(2n,1n), math.complex(1n,1n), math.complex(0n,1n)),
+            math.complex(1n,3n)))
+   })
+
 })
diff --git a/test/core/_dependencyExtractor.mjs b/test/core/dependencyExtractor.mjs
similarity index 89%
rename from test/core/_dependencyExtractor.mjs
rename to test/core/dependencyExtractor.mjs
index 91e0e40..bc1683f 100644
--- a/test/core/_dependencyExtractor.mjs
+++ b/test/core/dependencyExtractor.mjs
@@ -1,5 +1,5 @@
 import assert from 'assert'
-import dependencyExtractor from '../../src/core/dependencyExtractor.mjs'
+import {dependencyExtractor} from '../../src/core/extractors.mjs'
 
 describe('dependencyExtractor', () => {
    it('will record the keys of a destructuring function', () => {
diff --git a/test/custom.mjs b/test/custom.mjs
index 9fb66b1..6a399b0 100644
--- a/test/custom.mjs
+++ b/test/custom.mjs
@@ -8,6 +8,7 @@ import * as complex from '../src/complex/all.mjs'
 import * as complexAdd from '../src/complex/add.mjs'
 import * as complexNegate from '../src/complex/negate.mjs'
 import * as complexComplex from '../src/complex/complex.mjs'
+import * as bigintAdd from '../src/bigint/add.mjs'
 import * as concreteSubtract from '../src/generic/subtract.concrete.mjs'
 import * as genericSubtract from '../src/generic/subtract.mjs'
 import extendToComplex from '../src/complex/extendToComplex.mjs'
@@ -17,9 +18,10 @@ describe('A custom instance', () => {
    it("works when partially assembled", () => {
       bw.install(complex)
       // Not much we can call without any number types:
-      const i3 = {re: 0, im: 3}
-      assert.deepStrictEqual(bw.complex(0, 3), i3)
-      assert.deepStrictEqual(bw.chain(0).complex(3).value, i3)
+      assert.deepStrictEqual(bw.complex(undefined, undefined), undefined)
+      assert.deepStrictEqual(
+         bw.chain(undefined).complex(undefined).value,
+         undefined)
       // Don't have a way to negate things, for example:
       assert.throws(() => bw.negate(2), TypeError)
    })
@@ -33,7 +35,7 @@ describe('A custom instance', () => {
       assert.deepStrictEqual(
          bw.subtract(16, bw.add(3, bw.complex(0,4), 2)),
          math.complex(11, -4)) // note both instances coexist
-      assert.deepStrictEqual(bw.negate(math.complex(3, '8')).im, -8)
+      assert.deepStrictEqual(bw.negate(bw.complex(3, '8')).im, -8)
    })
 
    it("can be assembled piecemeal", () => {
@@ -112,4 +114,30 @@ describe('A custom instance', () => {
          math.complex(1n, -3n))
    })
 
+   it("instantiates templates correctly", () => {
+      const inst = new PocomathInstance('InstantiateTemplates')
+      inst.install(numberAdd)
+      inst.install({typeMerge: {'T,T': ({T}) => (t,u) => 'Merge to ' + T }})
+      assert.strictEqual(inst.typeMerge(7,6.28), 'Merge to number')
+      assert.strictEqual(inst.typeMerge(7,6), 'Merge to NumInt')
+      assert.strictEqual(inst.typeMerge(7.35,6), 'Merge to number')
+      inst.install(complexAdd)
+      inst.install(complexComplex)
+      inst.install(bigintAdd)
+      assert.strictEqual(
+         inst.typeMerge(6n, inst.complex(3n, 2n)),
+         'Merge to GaussianInteger')
+      assert.strictEqual(
+         inst.typeMerge(3, inst.complex(4.5,2.1)),
+         'Merge to Complex')
+      // The following is the current behavior, since 3 converts to 3+0i
+      // which is technically the same Complex type as 3n+0ni.
+      // This should clear up when Complex is templatized
+      assert.strictEqual(inst.typeMerge(3, inst.complex(3n)), 'Merge to Complex')
+      // But types that truly cannot be merged should throw a TypeError
+      // Should add a variation of this with a more usual type once there is
+      // one not interconvertible with others...
+      inst.install(genericSubtract)
+      assert.throws(() => inst.typeMerge(3, undefined), TypeError)
+   })
 })
diff --git a/test/tuple/_native.mjs b/test/tuple/_native.mjs
new file mode 100644
index 0000000..2cf56d1
--- /dev/null
+++ b/test/tuple/_native.mjs
@@ -0,0 +1,114 @@
+import assert from 'assert'
+import math from '../../src/pocomath.mjs'
+
+describe('tuple', () => {
+   it('can be created and provide its length', () => {
+      assert.strictEqual(math.length(math.tuple(3, 5.2, 2)), 3)
+   })
+
+   it('does not allow unification by converting consecutive arguments', () => {
+      assert.throws(() => math.tuple(3, 5.2, 2n), /TypeError.*unif/)
+      // Hence, the order matters in a slightly unfortunate way,
+      // but I think being a little ragged in these edge cases is OK:
+      assert.throws(
+         () => math.tuple(3, 2n, math.complex(5.2)),
+         /TypeError.*unif/)
+      assert.deepStrictEqual(
+         math.tuple(3, math.complex(2n), 5.2),
+         {elts: [math.complex(3), math.complex(2n), math.complex(5.2)]})
+   })
+
+   it('can be tested for zero and equality', () => {
+      assert.strictEqual(math.isZero(math.tuple(0,1)), false)
+      assert.strictEqual(math.isZero(math.tuple(0n,0n,0n,0n)), true)
+      assert.strictEqual(math.isZero(math.tuple(0,0.001,0)), false)
+      assert.deepStrictEqual(math.complex(0,0), {re: 0, im:0})
+      assert.strictEqual(math.isZero(math.tuple(0,math.complex(0,0))), true)
+      assert.strictEqual(
+         math.equal(
+            math.tuple(0,math.complex(0,0.1)),
+            math.complex(math.tuple(0,0), math.tuple(0,0.1))),
+         true)
+      assert.strictEqual(
+         math.equal(math.tuple(3n,2n), math.tuple(3,2)),
+         false)
+   })
+
+   it('supports addition', () => {
+      assert.deepStrictEqual(
+         math.add(math.tuple(3,4,5), math.tuple(2,1,0)),
+         math.tuple(5,5,5))
+      assert.deepStrictEqual(
+         math.add(math.tuple(3.25,4.5,5), math.tuple(3,3)),
+         math.tuple(6.25,7.5,5))
+      assert.deepStrictEqual(
+         math.add(math.tuple(math.complex(2,3), 7), math.tuple(4, 5, 6)),
+         math.tuple(math.complex(6,3), math.complex(12), math.complex(6)))
+      assert.deepStrictEqual(
+         math.add(math.tuple(5,6), 7),
+         math.tuple(12,6))
+      assert.deepStrictEqual(
+         math.add(math.tuple(math.complex(5,4),6), 7),
+         math.tuple(math.complex(12,4),math.complex(6)))
+   })
+
+   it('supports subtraction', () => {
+      assert.deepStrictEqual(
+         math.subtract(math.tuple(3n,4n,5n), math.tuple(2n,1n,0n)),
+         math.tuple(1n,3n,5n))
+      assert.throws(
+         () => math.subtract(math.tuple(5,6), math.tuple(7)),
+         /RangeError/)
+   })
+
+   it('makes a tuple of complex and conjugates it', () => {
+      const complexTuple = math.tuple(
+         math.complex(3,1), math.complex(4,2.2), math.complex(5,3))
+      assert.deepStrictEqual(
+         math.complex(math.tuple(3,4,5), math.tuple(1,2.2,3)),
+         complexTuple)
+      assert.deepStrictEqual(
+         math.conjugate(complexTuple),
+         math.tuple(math.complex(3,-1), math.complex(4,-2.2), math.complex(5,-3)))
+   })
+
+   it('supports division', () => {
+      assert.deepStrictEqual(
+         math.divide(math.tuple(3,4,5),math.tuple(1,2,2)),
+         math.tuple(3,2,2.5))
+   })
+
+   it('supports multiplication', () => {
+      assert.deepStrictEqual(
+         math.multiply(math.tuple(3,4,5), math.tuple(1,2,2)),
+         math.tuple(3,8,10))
+   })
+
+   it('supports one and zero', () => {
+      assert.deepStrictEqual(
+         math.one(math.tuple(2n,3n,0n)),
+         math.tuple(1n,1n,1n))
+      assert.deepStrictEqual(
+         math.zero(math.tuple(math.complex(5,2), 3.4)),
+         math.tuple(math.complex(0), math.complex(0)))
+   })
+
+   it('supports quotient and roundquotient', () => {
+      const bigTuple = math.tuple(1n,2n,3n,4n,5n)
+      const bigOnes = math.one(bigTuple)
+      const threes = math.add(bigOnes, bigOnes, bigOnes)
+      assert.deepStrictEqual(
+         math.quotient(bigTuple, threes),
+         math.tuple(0n, 0n, 1n, 1n, 1n))
+      assert.deepStrictEqual(
+         math.roundquotient(bigTuple, threes),
+         math.tuple(0n, 1n, 1n, 1n, 2n))
+   })
+
+   it('supports sqrt', () => {
+      assert.deepStrictEqual(
+         math.sqrt(math.tuple(4,-4,2.25)),
+         math.tuple(2, math.complex(0,2), 1.5))
+   })
+
+})