--- /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 "character/class_pt.ma".
+
+(* TRIPLES OF CHARACTER CLASSES *********************************************)
+
+lemma not_p_pS: ∀i. P i → P (i + 1) → False.
+#i #Hi #HSi
+elim (p_inv_gen … Hi) -Hi #hi #Hi
+elim (p_inv_gen … HSi) -HSi #hSi #HSi destruct
+lapply (injective_plus_l … HSi) -HSi #H
+elim (not_b_divides_nbr … H) -H //
+qed-.
+
+lemma not_p_pSS: ∀i. P i → P (i + 2) → False.
+#i #Hi #HSi
+elim (p_inv_gen … Hi) -Hi #hi #Hi
+elim (p_inv_gen … HSi) -HSi #hSi #HSi destruct
+>plus_plus_comm_23 in HSi; #H
+lapply (injective_plus_l … H) -H #H
+elim (not_b_divides_nbr … H) -H //
+qed-.
+
+lemma not_p_tS: ∀i. P i → T (i + 1) → False.
+#i #Hp #Ht
+elim (p_inv_gen … Hp) -Hp #hp #Hp
+elim (t_inv_gen … Ht) -Ht #ht #kt #Ht destruct
+>exp_n_m_plus_1 in Ht; <associative_times >associative_plus #H
+elim (not_b_divides_nbr … H) -H //
+qed-.