Section filter_map.
Variables A B C : Type.
Proof using.
induction l; intros; simpl in *.
- auto.
- repeat break_match; simpl; auto using f_equal.
Qed.

Lemma filterMap_ext :
forall (f g : A -> option B) l,
(forall x, f x = g x) ->
filterMap f l = filterMap g l.