proposition: Lemma ex_filterdiff_scal_l_fct : forall {F} {FF : Filter F} (x : V) (f : U -> K), ex_filterdiff f F -> ex_filterdiff (fun u => scal (f u) x) F.
proof: Proof. intros F FF x f [lf Df]. eexists. apply (filterdiff_scal_l_fct x) ; eassumption. Qed.
imports: Coq(Reals Psatz ssreflect) Rcomplements Rbar Lim_seq Iter Hierarchy Continuity Equiv