Module Type NZBaseProp (Import NZ : NZDomainSig').
Include BackportEq NZ NZ. (** eq_refl, eq_sym, eq_trans *)
(* TODO: how register ~= (which is just a notation) as a Symmetric relation, hence allowing "symmetry" tac ? *)

Theorem neq_sym : forall n m, n ~= m -> m ~= n.