Admitted. (* QuickChick plus_1_neq_0_firsttry. *)

(* Specifications: *)
Theorem negb_involutive : forall b : bool,
negb (negb b) = b. Admitted. (* QuickChick negb_involutive. *)
Theorem andb_commutative : forall b c, andb b c = andb c b.
Admitted. (* QuickChick andb_commutative. *)
Theorem andb_true_elim2 : forall b c : bool,
andb b c = true -> c = true.