| #V1 #V2 #T1 #T2 #_ #_ #IHV #IHT #f #X #H
elim (lifts_inv_flat1 … H) -H #W1 #U1 #HVW1 #HTU1 #H destruct
elim (IHV … HVW1) -V1 #W2 #HVW2 #HW12
- elim (IHT … HTU1) -T1 #U2 #HTU2 #HU12
+ elim (IHT … HTU1) -T1 #U2 #HTU2 #HU12
/3 width=5 by lifts_flat, tweq_cast, ex2_intro/
]
qed-.