40 Preliminaries
with the coefficients D'k and f3k en1erging frmn (83)-(84). The complete
posing of the problem consists of (83)-(85), which are supplemented with
the initial conditions
(86)
With the right and left differences 6 Vk
vk - Vk-l in the usual sense, the operator
can be factorized by letting
The equality L 1 L 2 1/k = L Yk holds true if
The same procedure works for eliminating /k and bk on the basis of formulae
(83)-(86).