proposition: Lemma sumMz : forall I r (P : pred I) F, (\sum_(i <- r | P i) F i)%N%:~R = \sum_(i <- r | P i) ((F i)%:~R) :> R.
proof: Proof. by apply: big_morph=> // x y; rewrite !pmulrn -rmorphD. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)