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Definition adhDa (D:R -> Prop) (a:R) : Prop :=
  forall alp:R, alp > 0 ->  exists x : R, D x /\ Rdist x a < alp.

Lemma limit_inv : forall (f:R -> R) (D:R -> Prop) (l x0:R), limit1_in f D l x0 -> l <> 0 -> limit1_in (fun x:R => / f x) D (/ l) x0.