Section Diff_comp.
Context {K : AbsRing} {U V W : NormedModule K}.

Lemma ex_filterdiff_comp
{F} {FF : Filter F} (f : U -> V) (g : V -> W) :
ex_filterdiff f F -> ex_filterdiff g (filtermap f F)
-> ex_filterdiff (fun y => g (f y)) F.