type Set a = [a]bool; function union(x: Set a, y: Set a) : Set a; axiom (forall x: Set a, y: Set a, z: a :: (x[z] || y[z]) == union(x, y)[z]); const intSet0: Set int; axiom (forall x: int :: intSet0[x] == (x == 0 || x == 2 || x == 3)); const intSet1: Set int; axiom (forall x: int :: intSet1[x] == (x == -5 || x == 3)); procedure P(); implementation P() { assert (forall x: int :: union(intSet0, intSet1)[x] == (x == -5 || x == 0 || x == 2 || x == 3)); } type Set a = [a]bool; function union(x: Set a, y: Set a) : Set a; axiom (forall x: Set a, y: Set a, z: a :: x[z] || y[z] <==> union(x, y)[z]); const intSet0: Set int; axiom (forall x: int :: intSet0[x] <==> x == 0 || x == 2 || x == 3); const intSet1: Set int; axiom (forall x: int :: intSet1[x] <==> x == -5 || x == 3); procedure P(); implementation P() { assert (forall x: int :: union(intSet0, intSet1)[x] <==> x == -5 || x == 0 || x == 2 || x == 3); } Boogie program verifier finished with 0 verified, 0 errors