sentences:  Shoenfield's theorem shows that if there is a model of ZF in which a given formula_3 statement φ is false, then φ is also false in the constructible universe of that model.In contrapositive, this means that if ZFC proves a formula_3 sentence then that sentence is also provable in ZF.The same argument can be applied to any other principle which always holds in the constructible universe, such as the combinatorial principle ◊.