On the index of operators with end symbol

A study was made in [1] of the class of one-dimensional singular integral-functional equations closely connected with elliptic boundary-value problems on the plane in domains with piecewise-smooth boundaries. A criterion for the Fredholm property of these operators was formulated there in terms of the so-called end symbol. This symbol is a semi-almost periodic matrix-valued function assigned to the equation under consideration. In this paper we study this situation from a more general point of view.