diff --git a/README.md b/README.md
index 26631ec..9277561 100644
--- a/README.md
+++ b/README.md
@@ -4,8 +4,10 @@ Proof of concepts for a PocoMath-adjacent approach to a possible math.ts (TypeSc
 
 Roadmap:
 
-1. Install over.ts and get an example of add with number and bigint implementations working with it.
-2. Use the builder pattern to get add working with its implmentations defined incrementally before producing the final overload.
+1. Install over.ts and get an example of add with number and bigint implementations working with it. [DONE]
+2. Use the builder pattern to get add working with its implmentations defined incrementally before producing the final overload. [Didn't quite work the way we wnated, but maybe we can do an alternative later.]
+3. Make a version of over.ts, call it util/overload.ts, that takes an array of implementations without redundant type annotation. [DONE]
+4. Improve that version of overload with rtti to select the implementation without the implementations having to throw errors. [IN PROGRESS]
 3. Use the builder pattern to get a single object with both an add and a negate method, with both defined incrementally, working.
 4. Incorporate a subtract method that works on numbers and bigint by separate definitions but with dependencies on add and negate.
 5. Incorporate a subtract method that works with one generic implementation that works for both number and bigint with dependencies on add and negate.
diff --git a/src/steps/three.ts b/src/steps/three.ts
new file mode 100644
index 0000000..e76253a
--- /dev/null
+++ b/src/steps/three.ts
@@ -0,0 +1,12 @@
+import overload from '../util/overload.js'
+
+const adder = overload([
+    (x: number, y: number) => {
+        if (typeof x === 'number' && typeof y === 'number') return x + y
+        throw new TypeError('Can only add numbers')
+    },
+    (x: string, y: string) => 'Yay' + x + y
+])
+
+console.log(adder(1, 2))
+console.log(adder('a', 'b'))
diff --git a/src/steps/two.ts b/src/steps/two.ts
new file mode 100644
index 0000000..6e47772
--- /dev/null
+++ b/src/steps/two.ts
@@ -0,0 +1,102 @@
+import { useTypes } from 'over.ts/src/index.js';
+
+const types = {
+   number: (x: unknown): x is number => typeof x === 'number',
+   bigint: (x: unknown): x is bigint => typeof x === 'bigint'
+}
+
+const overload = useTypes(types)
+
+type TypeName = keyof typeof types
+
+//type Tuple<T> = T | `${T}, ${Tuple<T>}`
+//type TypeTuple = Tuple<TypeName>
+
+type CheckTuple<T> = T extends TypeName
+  ? T
+  : T extends `${TypeName}, ${infer Rest}`
+  ? CheckTuple<Rest> extends string ? T : false
+  : false
+
+type CheckDecl<T> = T extends `${infer Args} -> ${TypeName}`
+  ? CheckTuple<Args> extends string ? T : never
+  : never
+
+function check<T extends string>(d: CheckDecl<T>) {
+  console.log(d)
+}
+
+check('number, bigint -> bigint')
+check('bigint -> number')
+
+// check('string -> number') // would be error as desired
+
+class ImpBuilder {
+  addImp<T extends string, U>(decl: CheckDecl<T>, imp: U) {
+    return Object.assign(this, {[decl]: imp} as Record<T, U>)
+  }
+//  finalize<T extends Record<string, unknown>>(this: T) {
+//    return overload(this as Omit<T, 'addImp' | 'finalize'>)
+  //  }
+  finalize() {
+    delete this.addImp
+    delete this.finalize
+    return this
+  }
+}
+
+function fixImps<T extends {addImp: any}>(imps: T): Omit<T, 'addImp'> {
+  const res = Object.assign({}, imps)
+  delete res.addImp
+  return res
+}
+
+function overloadImps<T>(imps: T) {
+  return overload(imps)
+}
+
+const negateImps = new ImpBuilder()
+  .addImp('number -> number', (a: number) => -a)
+  .addImp('bigint -> bigint', (a: bigint) => -a)
+
+const negate = overload(negateImps.finalize() as Omit<typeof negateImps, 'finalize'|'addImp'>)
+
+console.log('Negation of 5 is', negate(5))
+console.log('Negation of 5n is', negate(5n))
+
+const addImps = new ImpBuilder() // imagining this is in some "initialize a proto-bundle" file
+addImps.addImp('number, number -> number', (a: number, b: number) => a+b) // imagining this line in the `number` file
+const addAll = addImps.addImp('bigint, bigint -> bigint', (a: bigint, b: bigint) => a+b) // and this is in the `bigint` file
+const add = overload(addAll.finalize() as Omit<typeof addAll, 'finalize'|'addImp'>) // We wrap everything up elsewhere
+
+console.log('Sum of 5 and 7 is', add(5,7))
+console.log('Sum of 5n and 7n is', add(5n, 7n))
+
+try {
+    //@ts-expect-error
+    console.log('Mixed sum is', add(5n, 7))
+} catch {
+    console.log('Mixed sum errored as expected.')
+}
+
+/*****
+const addImps = new ImpBuilder()
+//addImps.addImp('number, number -> number', (a: number, b: number) => a+b)
+const subAddImps = addImps.addImp('number, number -> number', (a: number, b: number) => a+b).addImp('bigint, bigint -> bigint', (a: bigint, b: bigint) => {
+  console.log('adding bigints')
+  return a+b
+})
+//const finalAddImps = addImps.finalize()
+
+const add = overload(subAddImps.finalize() as Omit<typeof subAddImps, 'finalize'|'addImp'>)
+
+console.log('Sum of 5 and 7 is', add(5,7))
+console.log('Sum of 5n and 7n is', add(5n, 7n))
+
+try {
+    //@ts-expect-error
+    console.log('Mixed sum is', add(5n, 7))
+} catch {
+    console.log('Mixed sum errored as expected.')
+}
+****/
diff --git a/src/util/overload.ts b/src/util/overload.ts
new file mode 100644
index 0000000..71ab3fa
--- /dev/null
+++ b/src/util/overload.ts
@@ -0,0 +1,17 @@
+type UnionToIntersection<U> =
+    (U extends any ? (k: U) => void : never) extends ((k: infer I) => void)
+    ? I
+    : never;
+
+export default function overload<T extends readonly [...any[]]>(
+    imps: T): UnionToIntersection<T[number]> {
+    return <any>((...a: any[]) => {
+        for (let i = 0; i < imps.length; ++i) {
+            try {
+                const val = imps[i](...a)
+                return val
+            } catch {
+            }
+        }
+    })
+}
diff --git a/tsconfig.json b/tsconfig.json
index 5741128..99d3a5d 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -5,7 +5,8 @@
         "rootDir": "src",
         "outDir": "obj"
     },
-    "files": [
-        "src/steps/one.ts"
+    "include": [
+        "src/steps/three.ts",
+        "src/util/*.ts"
     ]
 }