proposition: Lemma domeq2_sym (f1 : U1) (f2 : U2) : dom_eq2 f1 f2 -> dom_eq2 f2 f1.
proof: Proof. by case/andP=>V D; apply/andP; rewrite (eqP V) (eqP D). Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)