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
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