Section Operations.
Context {K : AbsRing} {V : NormedModule K}.
Local Ltac plus_grab e :=
repeat rewrite (plus_assoc _ e) -(plus_comm e) -(plus_assoc e).

Lemma ex_filterdiff_scal_l : forall {F} {FF : Filter F} (x : V),
ex_filterdiff (fun k : K => scal k x) F.