Section Map_option.
Variable elt elt' : Type.
Variable f : key -> elt -> option elt'.
Hypothesis f_compat : forall x x' d, X.eq x x' -> f x d = f x' d.

Lemma map_option_2 : forall (m:t elt)(x:key),
In x (map_option f m) -> exists d, MapsTo x d m /\ f x d <> None.