tlt2.ts

const validGreeting: Greeting = `hi Jeff!` // 
// ✅ Result: 
//  note that the type of `validGreeting` is the union `"hi Jeff!" | "hi Maria!`
const invalidGreeting: Greeting = `bye Jeff!` // 
// ❌ Result: 
// Type '"bye Jeff!"' is not assignable to type '"hi Jeff!" | "hi Maria!"