proposition: Lemma nth_mul u p q k : nth (mul u p q) k = if (size p + size q).-1 <= k then C.zero else mul_coeff u p q k.
proof: Proof. by rewrite /nth /mul_trunc [in LHS]nth_mkseq_dflt. Qed.
imports: Coq(ZArith Reals) Coquelicot(Coquelicot) mathcomp.ssreflect(ssreflect ssrfun ssrbool eqtype ssrnat seq fintype bigop) Flocq(Core) Stdlib MathComp Interval Xreal Basic_rec