proposition: Lemma IDiv_strext : forall x y : subset I, (f x[/] g x[//]Hg x) [#] (f y[/] g y[//]Hg y) -> x [#] y.
proof: Proof. intros x y H. elim (div_strext _ _ _ _ _ _ _ H); intro H0; exact (csf_strext_unfolded _ _ _ _ _ H0). Qed.
imports: CoRN.ftc.PartFunEquality