lapply (drops_tls_at … Hf … HY) -Hf -HY #HY
elim (drops_inv_skip2 … HY) -HY #Z #K0 #HK01 #HZ #H destruct
elim (liftsb_inv_pair_sn … HZ) -HZ #V0 #HV10 #H destruct
lapply (drops_tls_at … Hf … HY) -Hf -HY #HY
elim (drops_inv_skip2 … HY) -HY #Z #K0 #HK01 #HZ #H destruct
elim (liftsb_inv_pair_sn … HZ) -HZ #V0 #HV10 #H destruct