Test.ts

/**
 * The type 'true' means a proof is satisfied.
 * The type 'never' means a proof is not satisfied.
 */

// Basic of this idea.

type AWrongProof = { x: number } extends { x: string } ? true : never

// Compile NG
// const aWrongProof: AWrongProof = true

// Above is samea as below.

const thatIsWrong: AWrongProof extends never ? true : never = true

// Let's introduce that alias.

type Not<A extends true | never> = A extends never ? true : never

const thatIsWrong0: Not<AWrongProof> = true
// Unfortunately, this says:
//    2322: Type 'boolean' is not assignable to type 'never'.

/**
 * Why?
 */