Section Operations_fct.
Context {K : AbsRing} {U V : NormedModule K}.

Lemma filterdiff_minus_fct {F} {FF : Filter F} (f g : U -> V) (lf lg : U -> V) :
filterdiff f F lf -> filterdiff g F lg ->
filterdiff (fun u => minus (f u) (g u)) F (fun u => minus (lf u) (lg u)).