Section CompLfun.
Variables (R : ringType) (wT aT vT rT : vectType R).
Implicit Types (f : 'Hom(vT, rT)) (g : 'Hom(aT, vT)) (h : 'Hom(wT, aT)).

Lemma limg_sum f I r (P : pred I) Us :
(f @: (\sum_(i <- r | P i) Us i) = \sum_(i <- r | P i) f @: Us i)%VS.