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_bst : forall m, bst m -> bst (map_option f m).
#[local]
Hint Resolve map_option_bst : core.