proposition: Lemma domeqVUn f1 f2 f1' f2' : dom_eq f1 f2 -> dom_eq f1' f2' -> valid (f1 \+ f1') -> valid (f2 \+ f2').
proof: Proof. by move=>D /(domeqVUnE D) ->. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)