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

Lemma filterdiff_comp
{F} {FF : Filter F} f g (lf : U -> V) (lg : V -> W) :
filterdiff f F lf -> filterdiff g (filtermap f F) lg
-> filterdiff (fun y => g (f y)) F (fun y => lg (lf y)).