Set.insert (Set.insert (Set.insert Set.empty 1) 2) 3 : Set Nat
fun x y => g { x := x, y := y } : Nat → Nat → Nat
fun x y => Set.insert (Set.insert Set.empty x) y : Nat → Nat → Set Nat
fun x y => { x := x, y := y } : Nat → Nat → Point