lapply (csx_fwd_pair_sn … H) #HW1
lapply (csx_fwd_flat_dx … H) #H1
@csx_appl_simple_theq /2 width=3 by simple_flat/ -IHV12b -HW1 -H1 #X #H1 #H2
-elim (cpxs_fwd_theta_vector … o … (V2@V2b) … H1) -H1 /2 width=1 by liftsv_cons/ -HV12b -HV12
+elim (cpxs_fwd_theta_vector … o … (V2⨮V2b) … H1) -H1 /2 width=1 by liftsv_cons/ -HV12b -HV12
[ -H #H elim H2 -H2 //
| -H2 /3 width=5 by csx_cpxs_trans, cpxs_flat_dx/
]