proposition: Lemma domeq2_trans (f1 : U1) (f2 : U2) (f3 : U3) : dom_eq2 f1 f2 -> dom_eq2 f2 f3 -> dom_eq2 f1 f3.
proof: Proof. by rewrite /dom_eq2=>/andP [/eqP -> /eqP ->]. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)