In the superfluidity problem treated on the basis of the Brueckner approach
implemented with a separable nucleon-nucleon potential, a method is develo
ped for solving the equation for the gag Delta in semi-infinite nuclear mat
ter. The proposed method relies on the concept of effective interaction act
ing in a model space where the equation for Delta is specified. This equati
on is recast into a simpler form such that Delta is expressed in terms of t
he quantity that has the meaning of an anomalous density in the model space
. The gap Delta proves nonlocal, and the corresponding Bogolyubov equations
are integro-differential. A method for numerically solving these equations
is developed and applied to several examples by way of illustration.