如何证明集合的补集是合合的?
Require Import Ensembles. Arguments In {_}. Arguments Complement {_}.
Variables (T:Type) (A:Ensemble T).
Axiom set_eq: forall (E1 E2:Ensemble T), (forall x, E1 x <-> E2 x) -> E1 = E2.
Lemma complement_involutive:
forall x, In (Complement (Complement A)) x -> In A x.
编辑:假设decidable (In A x)
能够firstorder
完全证明引理。