diff --git a/src/core/TypeDispatcher.js b/src/core/TypeDispatcher.js
index b763fde..23e1d54 100644
--- a/src/core/TypeDispatcher.js
+++ b/src/core/TypeDispatcher.js
@@ -151,7 +151,7 @@ export class TypeDispatcher {
          throw new ReferenceError(`no method or value for key '${key}'`)
       }
 
-      if (this.resolve._genDepsOf?.length) _addToDeps(key, types)
+      if (this.resolve._genDepsOf?.length) this._addToDeps(key, types)
 
       const behave = this._behaviors[key]
       if (behave.has(types)) return behave.get(types)
@@ -192,8 +192,6 @@ export class TypeDispatcher {
       try {
          theBehavior = item(DependencyRecorder(this, [], this), template)
       } catch {
-         // Didn't work as a factory, so guess we were wrong; just
-         // make this entity the behavior:
          behave.set(types, item)
          return item
       } finally {
@@ -201,6 +199,7 @@ export class TypeDispatcher {
       }
       if (typeof theBehavior === 'function'
           && theBehavior.length
+          && Array.isArray(template)
           && template.some(elt => Array.isArray(elt))
       ) {
          // have to wrap the behavior to collect the actual arguments
diff --git a/src/core/__test__/TypeDispatcher.spec.js b/src/core/__test__/TypeDispatcher.spec.js
index 2a61b17..009b8ef 100644
--- a/src/core/__test__/TypeDispatcher.spec.js
+++ b/src/core/__test__/TypeDispatcher.spec.js
@@ -1,9 +1,11 @@
 import assert from 'assert'
 import {TypeDispatcher} from '../TypeDispatcher.js'
 import {numbers} from '../../numbers.js'
+import {generics} from '../../generics.js'
 import {onType} from "#core/helpers.js"
 import {Any} from "#core/TypePatterns.js"
 import {Returns} from "#core/Type.js"
+import {plain} from "#number/helpers.js"
 
 describe('TypeDispatcher', () => {
    it('can build in stages', () => {
@@ -38,4 +40,11 @@ describe('TypeDispatcher', () => {
          incremental.add.resolve([Undefined, Number]).returns,
          Number)
    })
+   it('changes methods when their dependencies change', () => {
+      const gnmath = new TypeDispatcher(generics, numbers)
+      assert.strictEqual(gnmath.square(-2.5), 6.25)
+      // change multiplication of number to floor its first argument (?!)
+      gnmath.merge({multiply: plain((a,b) => Math.floor(a) * b)})
+      assert.strictEqual(gnmath.square(-2.5), 7.5)
+   })
 })
diff --git a/src/generic/__test__/arithmetic.spec.js b/src/generic/__test__/arithmetic.spec.js
new file mode 100644
index 0000000..f1d6043
--- /dev/null
+++ b/src/generic/__test__/arithmetic.spec.js
@@ -0,0 +1,11 @@
+import assert from 'assert'
+import math from '#nanomath'
+
+describe('generic arithmetic', () => {
+   it('squares anything', () => {
+      assert.strictEqual(math.square(7), 49)
+      assert.strictEqual(
+         math.square.resolve([math.types.Number]).returns,
+         math.types.Number)
+   })
+})
diff --git a/src/generic/all.js b/src/generic/all.js
new file mode 100644
index 0000000..0d39ba5
--- /dev/null
+++ b/src/generic/all.js
@@ -0,0 +1 @@
+export * as arithmetic from './arithmetic.js'
diff --git a/src/generic/arithmetic.js b/src/generic/arithmetic.js
new file mode 100644
index 0000000..433f373
--- /dev/null
+++ b/src/generic/arithmetic.js
@@ -0,0 +1,8 @@
+import {onType} from '#core/helpers.js'
+import {Returns} from '#core/Type.js'
+import {Any} from '#core/TypePatterns.js'
+
+export const square = onType(Any, (math, T) => {
+   const mult = math.multiply.resolve([T, T])
+   return Returns(mult.returns, a => mult(a, a))
+})
diff --git a/src/generics.js b/src/generics.js
new file mode 100644
index 0000000..0ce5d7b
--- /dev/null
+++ b/src/generics.js
@@ -0,0 +1 @@
+export * as generics from './generic/all.js'
diff --git a/src/nanomath.js b/src/nanomath.js
index ebb055e..c32247d 100644
--- a/src/nanomath.js
+++ b/src/nanomath.js
@@ -1,6 +1,7 @@
+import {generics} from './generics.js'
 import {numbers} from './numbers.js'
 import {TypeDispatcher} from '#core/TypeDispatcher.js'
 
-const math = new TypeDispatcher(numbers)
+const math = new TypeDispatcher(generics, numbers)
 
 export default math