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