Pencil of Lines on the \(2-D\) Torus

We consider the problem of finding the intersection points of a pencil of lines with rational slope on the \(2\)-dimensional torus. We show that the intersection points belonging to all the lines in the pencil form a finite cyclic group. We also exhibit a generator for this group in terms of the coefficients of the lines. The need for the results presented in this paper arose in dealing with a discrete limited angle model for computerized tomography \((Cf. [3], [5])\).