Definition MapsTo (k:key)(e:elt):= InA eqke (k,e).Definition In k m := exists e:elt, MapsTo k e m.Notation Sort := (sort ltk).Notation Inf := (lelistA ltk).

Lemma In_inv_3 : forall x x' l, InA eqke x (x' :: l) -> ~ eqk x x' -> InA eqke x l.