proposition: Lemma mxxMy t x y : valid (x \+ (mx t \+ y)) -> x \+ y = Unit.
proof: Proof. by rewrite joinCA=>/mxMx. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq) pcm(options prelude pred) pcm(pcm morphism natmap)