(** Relations between domination and equivalence *)

Lemma equiv_le_2 {T} {K : AbsRing} {V : NormedModule K}
F {FF : Filter F} (f g : T -> V) :
is_equiv F f g ->
F (fun x => norm (g x) <= 2 * norm (f x) /\ norm (f x) <= 2 * norm (g x)).