* //
qed.
+(* Basic inversions *********************************************************)
+
+lemma eq_inv_pnpred_bi:
+ injective … pnpred.
+#p1 #p2 #Hp
+>(npsucc_pred p1) >(npsucc_pred p2)
+<Hp -Hp @refl
+qed-.
+
(* Inversions with nsucc ****************************************************)
(*** nat_split *)