diff --git a/src/core/PocomathInstance.mjs b/src/core/PocomathInstance.mjs
index 901514b..0a589ca 100644
--- a/src/core/PocomathInstance.mjs
+++ b/src/core/PocomathInstance.mjs
@@ -319,7 +319,8 @@ export default class PocomathInstance {
                      `Conflicting definitions of ${signature} for ${name}`)
                }
             } else {
-               opImps[signature] = behavior
+               // Must avoid aliasing into another instance:
+               opImps[signature] = {uses: behavior.uses, does: behavior.does}
                for (const dep of behavior.uses) {
                   const depname = dep.split('(', 1)[0]
                   if (depname === 'self' || this._templateParam(depname)) {
@@ -402,80 +403,90 @@ export default class PocomathInstance {
       }
       Object.defineProperty(this, name, {configurable: true, value: 'limbo'})
       const tf_imps = {}
-      for (const [rawSignature, {uses, does}] of usableEntries) {
+      for (const [rawSignature, behavior] of usableEntries) {
          /* For now, replace theTemplateParam with 'any' */
          const signature = rawSignature.replaceAll(theTemplateParam, 'any')
-         if (uses.length === 0) {
-            tf_imps[signature] = does()
-         } else {
-            const refs = {}
-            let full_self_referential = false
-            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 = ''
-               if (func === 'self') {
-                  if (needsig) {
-                     if (full_self_referential) {
-                        throw new SyntaxError(
-                           'typed-function does not support mixed full and '
-                              + 'partial self-reference')
-                     }
-                     if (subsetOfKeys(typesOfSignature(needsig), this.Types)) {
-                        part_self_references.push(needsig)
-                     }
-                  } else {
-                     if (part_self_references.length) {
-                        throw new SyntaxError(
-                           'typed-function does not support mixed full and '
-                              + 'partial self-reference')
-                     }
-                     full_self_referential = true
-                  }
-               } else {
-                  if (this[func] === 'limbo') {
-                     /* We are in the midst of bundling func, so have to use
-                      * an indirect reference to func. And given that, there's
-                      * really no helpful way to extract a specific signature
-                      */
-                     const self = this
-                     refs[dep] = function () { // is this the most efficient?
-                        return self[func].apply(this, arguments)
-                     }
-                  } else {
-                     // can bundle up func, and grab its signature if need be
-                     let destination = this[func]
-                     if (needsig) {
-                        destination = this._typed.find(destination, needsig)
-                     }
-                     refs[dep] = destination
-                  }
-               }
-            }
-            if (full_self_referential) {
-               tf_imps[signature] = this._typed.referToSelf(self => {
-                  refs.self = self
-                  return does(refs)
-               })
-            } else if (part_self_references.length) {
-               tf_imps[signature] = this._typed.referTo(
-                  ...part_self_references, (...impls) => {
-                     for (let i = 0; i < part_self_references.length; ++i) {
-                        refs[`self(${part_self_references[i]})`] = impls[i]
-                     }
-                     return does(refs)
-                  }
-               )
-            } else {
-               tf_imps[signature] = does(refs)
-            }
-         }
+         this._addTFimplementation(
+            tf_imps, signature, behavior.uses, behavior.does)
       }
       const tf = this._typed(name, tf_imps)
       Object.defineProperty(this, name, {configurable: true, value: tf})
       return tf
    }
 
+   /* Adapts Pocomath-style behavior specification (uses, does) for signature
+    * to typed-function implementations and inserts the result into plain object
+    * imps
+    */
+   _addTFimplementation(imps, signature, uses, does) {
+      if (uses.length === 0) {
+         imps[signature] = does()
+         return
+      }
+      const refs = {}
+      let full_self_referential = false
+      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 = ''
+         if (func === 'self') {
+            if (needsig) {
+               if (full_self_referential) {
+                  throw new SyntaxError(
+                     'typed-function does not support mixed full and '
+                        + 'partial self-reference')
+               }
+               if (subsetOfKeys(typesOfSignature(needsig), this.Types)) {
+                  part_self_references.push(needsig)
+               }
+            } else {
+               if (part_self_references.length) {
+                  throw new SyntaxError(
+                     'typed-function does not support mixed full and '
+                        + 'partial self-reference')
+               }
+               full_self_referential = true
+            }
+         } else {
+            if (this[func] === 'limbo') {
+               /* We are in the midst of bundling func, so have to use
+                * an indirect reference to func. And given that, there's
+                * really no helpful way to extract a specific signature
+                */
+               const self = this
+               refs[dep] = function () { // is this the most efficient?
+                  return self[func].apply(this, arguments)
+               }
+            } else {
+               // can bundle up func, and grab its signature if need be
+               let destination = this[func]
+               if (needsig) {
+                  destination = this._typed.find(destination, needsig)
+               }
+               refs[dep] = destination
+            }
+         }
+      }
+      if (full_self_referential) {
+         imps[signature] = this._typed.referToSelf(self => {
+            refs.self = self
+            return does(refs)
+         })
+         return
+      }
+      if (part_self_references.length) {
+         imps[signature] = this._typed.referTo(
+            ...part_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)
+   }
 }