proposition: Lemma joinKx' (x1 x2 x : U) : x1 \+ x = x2 \+ x -> valid (x1 \+ x) -> x1 = x2.
proof: Proof. by move=>/[swap]; exact: joinKx. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq) pcm(options pred prelude) pcm(pcm unionmap natmap)