proposition: Lemma mxNN (x : mtx2) : valid x -> x != nown -> x = own.
proof: Proof. by case: x=>//; case=>//; case. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq) pcm(options prelude pred) pcm(pcm morphism natmap)