proposition: Lemma uunitL6 x : ujoin uunit x = x.
proof: Proof. by case: x=>*; rewrite /uunit /ujoin /= !unitL. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq bigop fintype finset) pcm(options axioms prelude seqperm pred seqext)