fix: Equal<A,B> with union types

The original implementation from `tyeppark` does not work with union type.

ts/predicates/Equal.spec.ts

@@ -1,6 +1,6 @@
 import { assertType, Equal, NotEqual } from '../index.js'
 
-describe('TypeEquals', () => {
+describe('Equal<A, B>', () => {
   test('match', () => {
     assertType.isTrue(true as Equal<false, false>)
   })
@@ -54,9 +54,14 @@ describe('TypeEquals', () => {
   test('overlap is false', () => {
     assertType.isFalse(false as Equal<{ a: 1, b: 1 }, { a: 1, c: 2 }>)
   })
+
+  it('works with union types', () => {
+    assertType.isTrue(true as Equal<{ a: number, b: string }, { a: number } & { b: string }>)
+    assertType.isTrue(true as Equal<{ a: number, b?: string }, { a: number } & { b?: string }>)
+  })
 })
 
-describe('TypeNotEquals', () => {
+describe('NotEqual<A, B>', () => {
   test('boolean', () => {
     assertType.isFalse(false as NotEqual<boolean, boolean>)
     assertType.isFalse(false as NotEqual<true, true>)
@@ -68,4 +73,8 @@ describe('TypeNotEquals', () => {
     assertType.isTrue(true as NotEqual<false, true>)
     assertType.isTrue(true as NotEqual<true, false>)
   })
+  it('works with union types', () => {
+    assertType.isFalse(false as NotEqual<{ a: number, b: string }, { a: number } & { b: string }>)
+    assertType.isTrue(true as NotEqual<{ a: number, b: string }, { a: number } & { b?: string }>)
+  })
 })

ts/predicates/Equal.ts

@@ -1,14 +1,23 @@
-/**
- * Checks if two types are equal.
- * Borrow from `typepark`.
- * The simple `A extends B ? B extends A ? true : false : false`
- * does not work with boolean type.
- */
-export type Equal<A, B, Then = true, Else = false> =
-  (<T>() => T extends A ? 1 : 2) extends (<T>() => T extends B ? 1 : 2)
-  ? Then : Else
-export type IsEqual<A, B> = Equal<A, B>
-
-export type NotEqual<A, B, Then = true, Else = false> =
-  (<T>() => T extends A ? 1 : 2) extends (<T>() => T extends B ? 1 : 2) ? Else : Then
-export type IsNotEqual<A, B> = NotEqual<A, B>
+/**
+ * `<T>() => T extends A ? 1 : 2` idea originate from `typepark`
+ * But it does not work with union types.
+ *
+ * `<T>() => T extends A` is a trick to create an inferred type `T`.
+ * This is needed for `boolean`, `string`, and `number`,
+ * as they supports literal types.
+ */
+
+/**
+ * Checks if two types are equal.
+ */
+export type Equal<A, B, Then = true, Else = false> =
+  [A, B] extends [object, object]
+  ? (A extends B ? B extends A ? Then : Else : Else)
+  : (<T>() => T extends A ? 1 : 2) extends (<T>() => T extends B ? 1 : 2) ? Then : Else
+export type IsEqual<A, B> = Equal<A, B>
+
+export type NotEqual<A, B, Then = true, Else = false> =
+  [A, B] extends [object, object]
+  ? (A extends B ? B extends A ? Else : Then : Then)
+  : (<T>() => T extends A ? 1 : 2) extends (<T>() => T extends B ? 1 : 2) ? Else : Then
+export type IsNotEqual<A, B> = NotEqual<A, B>