diff --git a/src/Updux.ts b/src/Updux.ts
index 2352b17..1bc0d37 100644
--- a/src/Updux.ts
+++ b/src/Updux.ts
@@ -18,23 +18,10 @@ import {
 import { withPayload } from './actions.js';
 import { AggregateActions, Dux, UnionToIntersection } from './types.js';
 import { buildActions } from './buildActions.js';
-import { buildInitial } from './buildInitial.js';
-
-type SubduxState<S> = 'initial' extends keyof S ? S['initial'] : {};
-
-type AggregateState<LOCAL, SUBDUXES extends Record<any, any>> = LOCAL &
-    (keyof SUBDUXES extends never
-        ? {}
-        : {
-              [Slice in keyof SUBDUXES]: Slice extends string
-                  ? SubduxState<SUBDUXES[Slice]>
-                  : never;
-          });
+import { buildInitial, AggregateState } from './initial.js';
 
 type MyActionCreator = { type: string } & ((...args: any) => any);
 
-type F = null extends any ? 'u' : 'n';
-
 type ResolveAction<
     ActionType extends string,
     ActionArg extends any,
@@ -69,33 +56,33 @@ export default class Updux<
     T_LocalActions extends {
         [actionType: string]: any;
     } = {},
-    SUBDUXES extends Record<string, Dux> = {},
+    T_Subduxes extends Record<string, Dux> = {},
 > {
     #localInitial: T_LocalState;
     #localActions: T_LocalActions;
     #localMutations: Record<
         string,
-        Mutation<ActionCreator<any>, AggregateState<T_LocalState, SUBDUXES>>
+        Mutation<ActionCreator<any>, AggregateState<T_LocalState, T_Subduxes>>
     > = {};
-    #subduxes: SUBDUXES;
+    #subduxes: T_Subduxes;
 
     #name: string;
 
-    #actions: AggregateActions<ResolveActions<T_LocalActions>, SUBDUXES>;
+    #actions: AggregateActions<ResolveActions<T_LocalActions>, T_Subduxes>;
 
-    #initial: AggregateState<T_LocalState, SUBDUXES>;
+    #initial: AggregateState<T_LocalState, T_Subduxes>;
 
     constructor(
         config: Partial<{
             initial: T_LocalState;
             actions: T_LocalActions;
-            subduxes: SUBDUXES;
+            subduxes: T_Subduxes;
         }>,
     ) {
         // TODO check that we can't alter the initial after the fact
         this.#localInitial = config.initial ?? ({} as T_LocalState);
         this.#localActions = config.actions ?? ({} as T_LocalActions);
-        this.#subduxes = config.subduxes ?? ({} as SUBDUXES);
+        this.#subduxes = config.subduxes ?? ({} as T_Subduxes);
 
         this.#actions = buildActions(this.#localActions, this.#subduxes);
 
@@ -128,7 +115,7 @@ export default class Updux<
     // TODO force the actionCreator to be one of the actions?
     mutation<A extends ActionCreator<any>>(
         actionCreator: A,
-        mutation: Mutation<A, AggregateState<T_LocalState, SUBDUXES>>,
+        mutation: Mutation<A, AggregateState<T_LocalState, T_Subduxes>>,
     ) {
         this.#localMutations[(actionCreator as any).type] = mutation;
     }
diff --git a/src/buildInitial.test.ts b/src/buildInitial.test.ts
index 7e8767e..63743e8 100644
--- a/src/buildInitial.test.ts
+++ b/src/buildInitial.test.ts
@@ -1,5 +1,5 @@
 import { test, expect } from 'vitest';
-import { buildInitial } from './buildInitial.js';
+import { buildInitial } from './initial.js';
 
 test('basic', () => {
     expect(
diff --git a/src/buildInitial.ts b/src/initial.ts
similarity index 52%
rename from src/buildInitial.ts
rename to src/initial.ts
index 7e2330e..36aaf92 100644
--- a/src/buildInitial.ts
+++ b/src/initial.ts
@@ -1,6 +1,17 @@
 import u from '@yanick/updeep-remeda';
 import * as R from 'remeda';
 
+type SubduxState<S> = 'initial' extends keyof S ? S['initial'] : {};
+
+export type AggregateState<LOCAL, SUBDUXES extends Record<any, any>> = LOCAL &
+    (keyof SUBDUXES extends never
+        ? {}
+        : {
+              [Slice in keyof SUBDUXES]: Slice extends string
+                  ? SubduxState<SUBDUXES[Slice]>
+                  : never;
+          });
+
 export function buildInitial(localInitial, subduxes) {
     if (Object.keys(subduxes).length > 0 && typeof localInitial !== 'object') {
         throw new Error(