+lemma lpx_sn_inv_pair: ∀R,I1,I2,L1,L2,V1,V2.
+ lpx_sn R (L1.ⓑ{I1}V1) (L2.ⓑ{I2}V2) →
+ ∧∧ lpx_sn R L1 L2 & R L1 V1 V2 & I1 = I2.
+#R #I1 #I2 #L1 #L2 #V1 #V2 #H elim (lpx_sn_inv_pair1 … H) -H
+#L0 #V0 #HL10 #HV10 #H destruct /2 width=1 by and3_intro/
+qed-.
+