--- /dev/null
+(**************************************************************************)
+(* ___ *)
+(* ||M|| *)
+(* ||A|| A project by Andrea Asperti *)
+(* ||T|| *)
+(* ||I|| Developers: *)
+(* ||T|| The HELM team. *)
+(* ||A|| http://helm.cs.unibo.it *)
+(* \ / *)
+(* \ / This file is distributed under the terms of the *)
+(* v GNU General Public License Version 2 *)
+(* *)
+(**************************************************************************)
+
+include "basics/logic.ma".
+
+axiom boh: (False → False) = True.
+
+definition J: False → False ≝ λf. match f in False with [ ].
+
+definition I2: True ≝ match boh with [ refl ⇒ J ].
+
+let rec err (u: True): False ≝ match u with [ I ⇒ err I2 ].
+
+lemma oops: False ≝ err I.