-lemma cpcs_bind_sn: ∀I,L,V1,V2,T. L ⊢ V1 ⬌* V2 → L ⊢ ⓑ{I}V1. T ⬌* ⓑ{I}V2. T.
-* /2 width=1/ /2 width=2/ qed.
+lemma cpcs_bind_sn: ∀a,I,L,V1,V2,T. L ⊢ V1 ⬌* V2 → L ⊢ ⓑ{a,I}V1. T ⬌* ⓑ{a,I}V2. T.
+#a * /2 width=1/ /2 width=2/ qed.
+
+lemma cpcs_beta_dx: ∀a,L,V1,V2,W,T1,T2.
+ L ⊢ V1 ➡ V2 → L.ⓛW ⊢ T1 ⬌* T2 → L ⊢ ⓐV1.ⓛ{a}W.T1 ⬌* ⓓ{a}V2.T2.
+#a #L #V1 #V2 #W #T1 #T2 #HV12 #HT12
+elim (cpcs_inv_cprs … HT12) -HT12 #T #HT1 #HT2
+lapply (cprs_beta_dx … HV12 HT1 a) -HV12 -HT1 #HT1
+lapply (cprs_lsubs_trans … HT2 (L.ⓓV2) ?) -HT2 /2 width=1/ #HT2
+@(cprs_div … HT1) /2 width=1/
+qed.
+
+lemma cpcs_beta_dx_tpr_rev: ∀a,L,V1,V2,W,T1,T2.
+ V1 ➡ V2 → L.ⓛW ⊢ T2 ⬌* T1 →
+ L ⊢ ⓓ{a}V2.T2 ⬌* ⓐV1.ⓛ{a}W.T1.
+/4 width=1/ qed.