proposition: Lemma cmU i j : U_(i)%M j = (i == j) :> nat.
proof: Proof. exact/ucmE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path choice finset fintype finfun) mathcomp(tuple bigop ssralg ssrint ssrnum) xfinmap