diff --git a/TODO.md b/TODO.md
index 58b23257..17199d52 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,6 +1,8 @@
-`NodeDefinition` should not have `rules` -- use `RuleDefinition`
+[mod] drop mod prefix of lookup
 
-`Node` should not have `definition` -- which is used to `getRule`
+`NodeDefinition.fullName`
+
+`Node` should not have `definition` -- which is used to `lookupRule`
 
 quit using `Action`
 
diff --git a/src/lang/definitions/NodeDefinition.ts b/src/lang/definitions/NodeDefinition.ts
index ffd1baf6..192e64cd 100644
--- a/src/lang/definitions/NodeDefinition.ts
+++ b/src/lang/definitions/NodeDefinition.ts
@@ -2,14 +2,11 @@ import { Definition } from "../definition"
 import { Net, Node, createNode } from "../graph"
 import { netConnect } from "../graph/netConnect"
 import { Mod } from "../mod"
-import { Rule } from "../rule"
 import { Type } from "../type"
 
 export type NodeKind = "Cons" | "Elim"
 
 export class NodeDefinition implements Definition {
-  private rules: Map<string, Rule> = new Map()
-
   constructor(
     public mod: Mod,
     public kind: NodeKind,
@@ -22,14 +19,6 @@ export class NodeDefinition implements Definition {
     return this.mod.url.href + "#" + this.name
   }
 
-  defineRule(end: NodeDefinition, rule: Rule): void {
-    this.rules.set(end.fullName, rule)
-  }
-
-  lookupRule(end: NodeDefinition): Rule | undefined {
-    return this.rules.get(end.fullName)
-  }
-
   build(): Node {
     return createNode(this.kind, this, this.input, this.output)
   }
diff --git a/src/lang/mod/Mod.ts b/src/lang/mod/Mod.ts
index ecc3a539..3274bbd4 100644
--- a/src/lang/mod/Mod.ts
+++ b/src/lang/mod/Mod.ts
@@ -1,6 +1,8 @@
 import { Definition } from "../definition"
+import { Rule } from "../rule"
 
 export type Mod = {
   url: URL
   definitions: Map<string, Definition>
+  rules: Map<string, Rule>
 }
diff --git a/src/lang/mod/createMod.ts b/src/lang/mod/createMod.ts
index 616da9cc..28b58ab2 100644
--- a/src/lang/mod/createMod.ts
+++ b/src/lang/mod/createMod.ts
@@ -4,8 +4,9 @@ import { defineBuiltInOperators } from "./defineBuiltInOperators"
 
 export function createMod(url: URL): Mod {
   const definitions: Map<string, Definition> = new Map()
+  const rules = new Map()
 
-  const mod = { url, definitions }
+  const mod = { url, definitions, rules }
 
   defineBuiltInOperators(mod)
 
diff --git a/src/lang/mod/defineRule.ts b/src/lang/mod/defineRule.ts
new file mode 100644
index 00000000..f5a9ab5c
--- /dev/null
+++ b/src/lang/mod/defineRule.ts
@@ -0,0 +1,21 @@
+import { Rule } from "../rule"
+import { Word } from "../word"
+import { Mod } from "./Mod"
+import { modLookupNodeDefinitionOrFail } from "./modLookupNodeDefinitionOrFail"
+
+export function defineRule(
+  mod: Mod,
+  start: string,
+  end: string,
+  words: Array<Word>,
+): void {
+  mod.rules.set(
+    `${start} ${end}`,
+    new Rule(
+      mod,
+      modLookupNodeDefinitionOrFail(mod, start),
+      modLookupNodeDefinitionOrFail(mod, end),
+      words,
+    ),
+  )
+}
diff --git a/src/lang/mod/modLookupRule.ts b/src/lang/mod/modLookupRule.ts
new file mode 100644
index 00000000..10564f74
--- /dev/null
+++ b/src/lang/mod/modLookupRule.ts
@@ -0,0 +1,10 @@
+import { Rule } from "../rule"
+import { Mod } from "./Mod"
+
+export function modLookupRule(
+  mod: Mod,
+  start: string,
+  end: string,
+): Rule | undefined {
+  return mod.rules.get(`${start} ${end}`)
+}
diff --git a/src/lang/mod/modLookupRuleByPorts.ts b/src/lang/mod/modLookupRuleByPorts.ts
index 2e8eba36..f12035e0 100644
--- a/src/lang/mod/modLookupRuleByPorts.ts
+++ b/src/lang/mod/modLookupRuleByPorts.ts
@@ -1,6 +1,7 @@
 import { Port } from "../graph"
 import { Rule } from "../rule"
 import { Mod } from "./Mod"
+import { modLookupRule } from "./modLookupRule"
 
 export function modLookupRuleByPorts(
   mod: Mod,
@@ -8,6 +9,6 @@ export function modLookupRuleByPorts(
   end: Port,
 ): Rule | undefined {
   if (start.isPrincipal && end.isPrincipal) {
-    return start.node.definition.lookupRule(end.node.definition)
+    return modLookupRule(mod, start.node.name, end.node.name)
   }
 }
diff --git a/src/lang/stmts/Defrule.ts b/src/lang/stmts/Defrule.ts
index bf01e68e..cdcf61db 100644
--- a/src/lang/stmts/Defrule.ts
+++ b/src/lang/stmts/Defrule.ts
@@ -1,6 +1,5 @@
 import { Mod } from "../mod"
-import { modLookupNodeDefinitionOrFail } from "../mod/modLookupNodeDefinitionOrFail"
-import { Rule } from "../rule"
+import { defineRule } from "../mod/defineRule"
 import { Span } from "../span"
 import { Stmt } from "../stmt"
 import { Word } from "../word"
@@ -14,12 +13,6 @@ export class Defrule implements Stmt {
   ) {}
 
   async execute(mod: Mod): Promise<void> {
-    const startNodeDefinition = modLookupNodeDefinitionOrFail(mod, this.start)
-    const endNodeDefinition = modLookupNodeDefinitionOrFail(mod, this.end)
-
-    startNodeDefinition.defineRule(
-      endNodeDefinition,
-      new Rule(mod, startNodeDefinition, endNodeDefinition, this.words),
-    )
+    defineRule(mod, this.start, this.end, this.words)
   }
 }