Arguments submxP {m1 m2 n A B}.

Lemma summx_sub m1 m2 n (B : 'M_(m2, n))
I (r : seq I) (P : pred I) (A_ : I -> 'M_(m1, n)) :
(forall i, P i -> A_ i <= B)%MS -> ((\sum_(i <- r | P i) A_ i)%R <= B)%MS.