proposition: Lemma size_drop_poly n p : size (drop_poly n p) = (size p - n)%N.
proof: Proof. have [pLn|nLp] := leqP (size p) n. by rewrite (eqP pLn) drop_poly_eq0 ?size_poly0. have p_neq0 : p != 0 by rewrite -size_poly_gt0 (leq_trans _ nLp). by rewrite size_poly_eq// predn_sub subnK ?lead_coef_eq0// -ltnS -polySpred. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)