This lifetable identity is the same no matter what kind of lifetable is required. You can find it in any demography textbook.
lt_id_d_l(ndx, radix = sum(ndx))
numeric. Vector of age-specific lifetable deaths.
lx vector of lifetable survivorship
The vector returned is the same length as
dx and it sums to the lifetable radix. If the radix is one then this is the discrete deaths distribution.
Preston S, Heuveline P, Guillot M (2000). Demography: measuring and modeling population processes. Wiley-Blackwell.