proposition: Lemma rect s : s = \sum_(i < n | (i < sig1 s)%N) p_ i + sig2 s :> nat.
proof: Proof. by rewrite -[s]sigK rankEsum /= sigK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)