L ⊢ ⓑ{I} V1. T1 ➡ ⓑ{I} V2. T2.
#I #L #V1 #V2 #T1 #T2 #HV12 * #T #HT1 normalize #HT2
elim (tpss_split_up … HT2 1 ? ?) -HT2 // #T0 <minus_n_O #HT0 normalize <minus_plus_m_m #HT02
-lapply (tpss_lsubs_conf … HT0 (⋆. ⓑ{I} V2) ?) -HT0 /2 width=1/ #HT0
-lapply (tpss_tps … HT0) -HT0 #HT0
+lapply (tpss_lsubs_trans … HT0 (⋆. ⓑ{I} V2) ?) -HT0 /2 width=1/ #HT0
+lapply (tpss_inv_SO2 … HT0) -HT0 #HT0
@ex2_1_intro [2: @(tpr_delta … HV12 HT1 HT0) | skip | /2 width=1/ ] (**) (* /3 width=5/ is too slow *)
qed.