proposition: Lemma mnmwidenD m1 m2 : mnmwiden (m1 + m2) = (mnmwiden m1 + mnmwiden m2)%MM.
proof: Proof. apply/mnmP=> i; rewrite mnmDE !multinomE !(tnth_nth 0%N) /=. rewrite !nth_rcons size_map size_enum_ord !size_tuple !if_same. case h: (i < n); last by rewrite addn0. rewrite (nth_map (Ordinal h)) ?size_enum_ord //. by rewrite !(mnm_nth 0%N) /= !nth_enum_ord. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finfun bigop finset binomial) mathcomp(order fingroup perm ssralg zmodp poly ssrint) mathcomp(matrix vector) mathcomp(bigenough) ssrcomplements freeg