(* bug. intros k deve fare whd quanto basta *)
intros 6 (E x y z Exy Eyz); intro Axy; cases (ap_cotransitive ???y Axy);
[apply Exy|apply Eyz] assumption.
qed.
(* bug. intros k deve fare whd quanto basta *)
intros 6 (E x y z Exy Eyz); intro Axy; cases (ap_cotransitive ???y Axy);
[apply Exy|apply Eyz] assumption.
qed.