proposition: Lemma domeq0E f : dom_eq f Unit -> f = Unit.
proof: Proof. by case/domeqP; rewrite valid_unit dom0; apply: dom0E. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)