  The tensorial form of the spin-other-orbit interaction operator in the
formalism of second quantization is presented. Such an expression is needed to
calculate both diagonal and off-diagonal matrix elements according to an
approach, based on a combination of second quantization in the coupled
tensorial form, angular momentum theory in three spaces (orbital, spin and
quasispin), and a generalized graphical technique. One of the basic features of
this approach is the use of tables of standard quantities, without which the
process of obtaining matrix elements of spin-other-orbit interaction operator
between any electron configurations is much more complicated. Some special
cases are shown for which the tensorial structure of the spin-other-orbit
interaction operator reduces to an unusually simple form.
