proposition: Lemma inverse_undef : inverse undef = undef.
proof: Proof. by rewrite /inverse umfoldl_undef. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)