proposition: Lemma assocs_undef : assocs (undef : U) = [::].
proof: Proof. by rewrite /undef /= !umEX. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)