diff --git a/bigint/BigInt.mjs b/bigint/BigInt.mjs
deleted file mode 100644
index c1d60d1..0000000
--- a/bigint/BigInt.mjs
+++ /dev/null
@@ -1,3 +0,0 @@
-import typed from 'typed-function'
-
-typed.addType({name: 'bigint', test: b => typeof b === 'bigint'})
diff --git a/complex/add.mjs b/complex/add.mjs
deleted file mode 100644
index 9cefa0a..0000000
--- a/complex/add.mjs
+++ /dev/null
@@ -1,15 +0,0 @@
-import {numComplex} from './types/Complex.mjs'
-
-export const add = {
-   '...Complex': [['self'], ref => addends => {
-      if (addends.length === 0) return {re:0, im:0}
-      const seed = addends.shift()
-      return addends.reduce((w,z) => {
-         /* Need a "base case" to avoid infinite self-reference loops */
-         if (numComplex(z) && numComplex(w)) {
-            return {re: w.re + z.re, im: w.im + z.im}
-         }
-         return {re: ref.self(w.re, z.re), im: ref.self(w.im, z.im)}
-      }, seed)
-   }]
-}
diff --git a/complex/negate.mjs b/complex/negate.mjs
deleted file mode 100644
index 77dfb01..0000000
--- a/complex/negate.mjs
+++ /dev/null
@@ -1,8 +0,0 @@
-import {numComplex} from './types/Complex.mjs'
-export const negate = {
-   Complex: [['self'], ref => z => {
-      /* need a "base case" to avoid infinite self-reference */
-      if (numComplex(z)) return {re: -z.re, im: -z.im}
-      return {re: ref.self(z.re), im: ref.self(z.im)}
-   }]
-}
diff --git a/number/negate.mjs b/number/negate.mjs
deleted file mode 100644
index b9a73cb..0000000
--- a/number/negate.mjs
+++ /dev/null
@@ -1,3 +0,0 @@
-export const negate = {
-   number: [[], n => -n]
-}
diff --git a/package.json5 b/package.json5
index 6c804ce..f83ee88 100644
--- a/package.json5
+++ b/package.json5
@@ -5,7 +5,9 @@
     inclusion, avoiding factory functions.',
   main: 'index.js',
   scripts: {
-    test: '!(find . | sort -f | uniq -i -c | grep -v " 1 ") && npx mocha',
+    'test:filecase': '!(find . | sort -f | uniq -i -c | grep -v " 1 ")',
+    'test:unit': 'npx mocha --recursive',
+    test: 'pnpm test:filecase && pnpm test:unit',
   },
   repository: {
     type: 'git',
diff --git a/src/bigint/Types/bigint.mjs b/src/bigint/Types/bigint.mjs
new file mode 100644
index 0000000..45ece8f
--- /dev/null
+++ b/src/bigint/Types/bigint.mjs
@@ -0,0 +1,3 @@
+export const Types = {
+    bigint: {test: b => typeof b === 'bigint'}
+}
diff --git a/bigint/add.mjs b/src/bigint/add.mjs
similarity index 68%
rename from bigint/add.mjs
rename to src/bigint/add.mjs
index 6bb1282..d6fc0c7 100644
--- a/bigint/add.mjs
+++ b/src/bigint/add.mjs
@@ -1,4 +1,5 @@
-import './BigInt.mjs'
+export {Types} from './Types/bigint.mjs'
+
 export const add = {
    '...bigint': [[], addends => addends.reduce((x,y) => x+y, 0n)],
 }
diff --git a/number/all.mjs b/src/bigint/all.mjs
similarity index 73%
rename from number/all.mjs
rename to src/bigint/all.mjs
index 395eb54..f4cdb60 100644
--- a/number/all.mjs
+++ b/src/bigint/all.mjs
@@ -1,3 +1,4 @@
+export {Types} from './Types/bigint.mjs'
 export {add} from './add.mjs'
 export {negate} from './negate.mjs'
 export {subtract} from '../generic/subtract.mjs'
diff --git a/bigint/negate.mjs b/src/bigint/negate.mjs
similarity index 52%
rename from bigint/negate.mjs
rename to src/bigint/negate.mjs
index ec89bac..538e1d4 100644
--- a/bigint/negate.mjs
+++ b/src/bigint/negate.mjs
@@ -1,2 +1,3 @@
-import './BigInt.mjs'
+export {Types} from './Types/bigint.mjs'
+
 export const negate = {bigint: [[], b => -b ]}
diff --git a/complex/types/Complex.mjs b/src/complex/Types/Complex.mjs
similarity index 53%
rename from complex/types/Complex.mjs
rename to src/complex/Types/Complex.mjs
index 86879fb..e3f29e1 100644
--- a/complex/types/Complex.mjs
+++ b/src/complex/Types/Complex.mjs
@@ -1,5 +1,3 @@
-import typed from 'typed-function'
-
 /* Use a plain object with keys re and im for a complex; note the components
  * can be any type (for this proof-of-concept; in reality we'd want to
  * insist on some numeric or scalar supertype).
@@ -8,20 +6,13 @@ export function isComplex(z) {
    return z && typeof z === 'object' && 're' in z && 'im' in z
 }
 
-typed.addType({name: 'Complex', test: isComplex})
-typed.addConversion({
-   from: 'number',
-   to: 'Complex',
-   convert: x => ({re: x, im: 0})
-})
-/* Pleasantly enough, it is OK to add this conversion even if there is no
- * type 'bigint' defined, so everything should Just Work.
- */
-typed.addConversion({
-   from: 'bigint',
-   to: 'Complex',
-   convert: x => ({re: x, im: 0n})
-})
+export const Types = {
+   Complex: {
+      test: isComplex,
+      number: x => ({re: x, im: 0}),
+      bigint: x => ({re: x, im: 0n})
+   }
+}
 
 /* test if an entity is Complex<number>, so to speak: */
 export function numComplex(z) {
diff --git a/src/complex/add.mjs b/src/complex/add.mjs
new file mode 100644
index 0000000..3583b38
--- /dev/null
+++ b/src/complex/add.mjs
@@ -0,0 +1,10 @@
+export {Types} from './Types/Complex.mjs'
+
+export const add = {
+   '...Complex': [['self'], ref => addends => {
+      if (addends.length === 0) return {re:0, im:0}
+      const seed = addends.shift()
+      return addends.reduce((w,z) =>
+         ({re: ref.self(w.re, z.re), im: ref.self(w.im, z.im)}), seed)
+   }]
+}
diff --git a/complex/all.mjs b/src/complex/all.mjs
similarity index 78%
rename from complex/all.mjs
rename to src/complex/all.mjs
index ebd9375..d5d5bda 100644
--- a/complex/all.mjs
+++ b/src/complex/all.mjs
@@ -1,3 +1,4 @@
+export {Types} from './Types/Complex.mjs'
 export {complex} from './complex.mjs'
 export {add} from './add.mjs'
 export {negate} from './negate.mjs'
diff --git a/complex/complex.mjs b/src/complex/complex.mjs
similarity index 88%
rename from complex/complex.mjs
rename to src/complex/complex.mjs
index 9d7f0c5..c86c3e8 100644
--- a/complex/complex.mjs
+++ b/src/complex/complex.mjs
@@ -1,4 +1,4 @@
-import './types/Complex.mjs'
+export {Types} from './Types/Complex.mjs'
 
 export const complex = {
    /* Very permissive for sake of proof-of-concept; would be better to
diff --git a/complex/extendToComplex.mjs b/src/complex/extendToComplex.mjs
similarity index 94%
rename from complex/extendToComplex.mjs
rename to src/complex/extendToComplex.mjs
index 64f4736..21e1a29 100644
--- a/complex/extendToComplex.mjs
+++ b/src/complex/extendToComplex.mjs
@@ -1,4 +1,3 @@
-import './types/Complex.mjs'
 import * as complex from './complex.mjs'
 
 /* Add all the complex implementations for functions already
diff --git a/src/complex/negate.mjs b/src/complex/negate.mjs
new file mode 100644
index 0000000..bf4e612
--- /dev/null
+++ b/src/complex/negate.mjs
@@ -0,0 +1,7 @@
+export {Types} from './Types/Complex.mjs'
+
+export const negate = {
+   Complex: [['self'], ref => z => {
+      return {re: ref.self(z.re), im: ref.self(z.im)}
+   }]
+}
diff --git a/PocomathInstance.mjs b/src/core/PocomathInstance.mjs
similarity index 68%
rename from PocomathInstance.mjs
rename to src/core/PocomathInstance.mjs
index facdfb4..307f832 100644
--- a/PocomathInstance.mjs
+++ b/src/core/PocomathInstance.mjs
@@ -6,6 +6,10 @@ export default class PocomathInstance {
       this.name = name
       this._imps = {}
       this._affects = {}
+      this._typed = typed.create()
+      this._typed.clear()
+      // Convenient hack for now, would remove when a real string type is added:
+      this._typed.addTypes([{name: 'string', test: s => typeof s === 'string'}])
    }
     
    /**
@@ -29,7 +33,14 @@ export default class PocomathInstance {
     *    by the signature and returning the value. Otherwise, it should be
     *    a function taking an object with the dependency lists as keys and the
     *    requested functions as values, to a function taking the arguments
-    *    specified by the signature and returning the value
+    *    specified by the signature and returning the value.
+    *
+    *    Note that the "operation" named `Types` is special: it gives
+    *    types that must be installed in the instance. In this case, the keys
+    *    are type names, and the values are objects with a property 'test'
+    *    giving the predicate for the type, and properties for each type that can
+    *    be converted **to** this type, giving the corresponding conversion
+    *    function.
     */
    install(ops) {
       for (const key in ops) this._installOp(key, ops[key])
@@ -47,7 +58,7 @@ export default class PocomathInstance {
                `Conflicting definitions of ${signature} for ${name}`)
          } else {
             opImps[signature] = implementations[signature]
-            for (const dep of implementations[signature][0]) {
+            for (const dep of implementations[signature][0] || []) {
                const depname = dep.split('(', 1)[0]
                if (depname === 'self') continue
                if (!(depname in this._affects)) {
@@ -87,6 +98,7 @@ export default class PocomathInstance {
       if (!imps || Object.keys(imps).length === 0) {
          throw new SyntaxError(`No implementations for ${name}`)
       }
+      this._ensureTypes()
       const tf_imps = {}
       for (const signature in imps) {
          const [deps, imp] = imps[signature]
@@ -107,7 +119,7 @@ export default class PocomathInstance {
                }
             }
             if (self_referential) {
-               tf_imps[signature] = typed.referToSelf(self => {
+               tf_imps[signature] = this._typed.referToSelf(self => {
                   refs.self = self
                   return imp(refs)
                })
@@ -116,7 +128,7 @@ export default class PocomathInstance {
             }
          }
       }
-      const tf = typed(name, tf_imps)
+      const tf = this._typed(name, tf_imps)
       this[name] = tf
       return tf
    }
@@ -127,7 +139,40 @@ export default class PocomathInstance {
     */
    _ensureBundle(name) {
       const maybe = this[name]
-      if (typed.isTypedFunction(maybe)) return maybe
+      if (this._typed.isTypedFunction(maybe)) return maybe
       return this._bundle(name)
    }
+
+   /**
+    * Ensure that all of the requested types and conversions are actually
+    * in the typed-function universe:
+    */
+   _ensureTypes() {
+      const newTypes = []
+      const newTypeSet = new Set()
+      const knownTypeSet = new Set()
+      const conversions = []
+      const typeSpec = this._imps.Types
+      for (const name in this._imps.Types) {
+         knownTypeSet.add(name)
+         for (const from in typeSpec[name]) {
+            if (from === 'test') continue;
+            conversions.push(
+               {from, to: name, convert: typeSpec[name][from]})
+         }
+         try { // Hack: work around typed-function #154
+            this._typed._findType(name)
+         } catch {
+            newTypeSet.add(name)
+            newTypes.push({name, test: typeSpec[name].test})
+         }
+      }
+      this._typed.addTypes(newTypes)
+      const newConversions = conversions.filter(
+         item => (newTypeSet.has(item.from) || newTypeSet.has(item.to)) &&
+            knownTypeSet.has(item.from) && knownTypeSet.has(item.to)
+      )
+      this._typed.addConversions(newConversions)
+   }
+
 }
diff --git a/generic/subtract.mjs b/src/generic/subtract.mjs
similarity index 100%
rename from generic/subtract.mjs
rename to src/generic/subtract.mjs
diff --git a/src/number/Types/number.mjs b/src/number/Types/number.mjs
new file mode 100644
index 0000000..40e390b
--- /dev/null
+++ b/src/number/Types/number.mjs
@@ -0,0 +1,7 @@
+export const Types = {
+    number: {
+        test: n => typeof n === 'number',
+        string: s => +s
+    }
+}
+
diff --git a/number/add.mjs b/src/number/add.mjs
similarity index 67%
rename from number/add.mjs
rename to src/number/add.mjs
index 49c1f40..70be9bb 100644
--- a/number/add.mjs
+++ b/src/number/add.mjs
@@ -1,3 +1,5 @@
+export {Types} from './Types/number.mjs'
+
 export const add = {
    '...number': [[], addends => addends.reduce((x,y) => x+y, 0)],
 }
diff --git a/bigint/all.mjs b/src/number/all.mjs
similarity index 73%
rename from bigint/all.mjs
rename to src/number/all.mjs
index 395eb54..bf737f5 100644
--- a/bigint/all.mjs
+++ b/src/number/all.mjs
@@ -1,3 +1,4 @@
+export {Types} from './Types/number.mjs'
 export {add} from './add.mjs'
 export {negate} from './negate.mjs'
 export {subtract} from '../generic/subtract.mjs'
diff --git a/src/number/negate.mjs b/src/number/negate.mjs
new file mode 100644
index 0000000..aaf8bc0
--- /dev/null
+++ b/src/number/negate.mjs
@@ -0,0 +1,3 @@
+export { Types } from './Types/number.mjs'
+
+export const negate = {number: [[], n => -n]}
diff --git a/pocomath.mjs b/src/pocomath.mjs
similarity index 84%
rename from pocomath.mjs
rename to src/pocomath.mjs
index 5a9bd4a..c5a81d4 100644
--- a/pocomath.mjs
+++ b/src/pocomath.mjs
@@ -1,5 +1,5 @@
 /* Core of pocomath: generates the default instance */
-import PocomathInstance from './PocomathInstance.mjs'
+import PocomathInstance from './core/PocomathInstance.mjs'
 import * as numbers from './number/all.mjs'
 import * as bigints from './bigint/all.mjs'
 import * as complex from './complex/all.mjs'
diff --git a/test/_pocomath.mjs b/test/_pocomath.mjs
index af24836..507d811 100644
--- a/test/_pocomath.mjs
+++ b/test/_pocomath.mjs
@@ -1,5 +1,5 @@
 import assert from 'assert'
-import math from '../pocomath.mjs'
+import math from '../src/pocomath.mjs'
 
 describe('The default full pocomath instance "math"', () => {
    it('can subtract numbers', () => {
diff --git a/test/_PocomathInstance.mjs b/test/core/_PocomathInstance.mjs
similarity index 87%
rename from test/_PocomathInstance.mjs
rename to test/core/_PocomathInstance.mjs
index d48cfd8..28176e2 100644
--- a/test/_PocomathInstance.mjs
+++ b/test/core/_PocomathInstance.mjs
@@ -1,5 +1,5 @@
 import assert from 'assert'
-import PocomathInstance from '../PocomathInstance.mjs'
+import PocomathInstance from '../../src/core/PocomathInstance.mjs'
 
 describe('PocomathInstance', () => {
    it('creates an instance that can define typed-functions', () => {
diff --git a/test/custom.mjs b/test/custom.mjs
index a9d3df2..aabbb8c 100644
--- a/test/custom.mjs
+++ b/test/custom.mjs
@@ -1,26 +1,26 @@
 import assert from 'assert'
-import math from '../pocomath.mjs'
-import typed from 'typed-function'
-import PocomathInstance from '../PocomathInstance.mjs'
-import * as numbers from '../number/all.mjs'
-import * as numberAdd from '../number/add.mjs'
-import * as complex from '../complex/all.mjs'
-import * as complexAdd from '../complex/add.mjs'
-import * as complexNegate from '../complex/negate.mjs'
-import extendToComplex from '../complex/extendToComplex.mjs'
+import math from '../src/pocomath.mjs'
+import PocomathInstance from '../src/core/PocomathInstance.mjs'
+import * as numbers from '../src/number/all.mjs'
+import * as numberAdd from '../src/number/add.mjs'
+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 extendToComplex from '../src/complex/extendToComplex.mjs'
 
 const bw = new PocomathInstance('backwards')
 describe('A custom instance', () => {
    it("works when partially assembled", () => {
       bw.install(complex)
-      assert.deepStrictEqual(bw.add(2, bw.complex(0, 3)), {re: 2, im: 3})
-      assert.deepStrictEqual(bw.negate(2), bw.complex(-2,-0))
-      assert.deepStrictEqual(bw.subtract(2, bw.complex(0, 3)), {re: 2, im: -3})
+      // Not much we can call without any number types:
+      assert.deepStrictEqual(bw.complex(0, 3), {re: 0, im: 3})
+      // Don't have a way to negate things, for example:
+      assert.throws(() => bw.negate(2), TypeError)
    })
 
    it("can be assembled in any order", () => {
       bw.install(numbers)
-      typed.addConversion({from: 'string', to: 'number', convert: x => +x})
+      bw.install({Types: {string: {test: s => typeof s === 'string'}}})
       assert.strictEqual(bw.subtract(16, bw.add(3,4,2)), 7)
       assert.strictEqual(bw.negate('8'), -8)
       assert.deepStrictEqual(bw.add(bw.complex(1,3), 1), {re: 2, im: 3})
@@ -36,7 +36,7 @@ describe('A custom instance', () => {
       assert.strictEqual(pm.subtract(5, 10), -5)
       pm.install(complexAdd)
       pm.install(complexNegate)
-      // Should be enough to allow complex subtraction, as subtract is generic
+      // Should be enough to allow complex subtraction, as subtract is generic:
       assert.deepStrictEqual(
          pm.subtract({re:5, im:0}, {re:10, im:1}), {re:-5, im: -1})
    })
@@ -45,8 +45,9 @@ describe('A custom instance', () => {
       const cherry = new PocomathInstance('cherry')
       cherry.install(numberAdd)
       await extendToComplex(cherry)
-      // Now we have an instance that supports addition for number and complex
-      // and little else:
+      /* Now we have an instance that supports addition for number and complex
+         and little else:
+      */
       assert.strictEqual(cherry.add(3, 4, 2), 9)
       assert.deepStrictEqual(
          cherry.add(cherry.complex(3, 3), 4, cherry.complex(2, 2)),