inversion H.
assumption.
Qed.

(* Specifications: *)
Lemma IfProp_false : forall A B:Prop, IfProp A B false -> B.
intros A B H.
Lemma IfProp_or : forall (A B:Prop) (b:bool), IfProp A B b -> A \/ B.
destruct 1; auto with bool.