proposition: Lemma sigE12 s : sig s = @Tagged _ (sig1 s) _ (sig2 s).
proof: Proof. by rewrite /sig1 /sig2; case: sig. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)