Many problems of the engineering sciences, physics, and mathematics lead
to con- volution equations and their various modifications. Convolution
equations on a half-line can be studied by having recourse to the
methods and results of the theory of Toeplitz and Wiener-Hopf operators.
Convolutions by integrable kernels have continuous symbols and the
Cauchy singular integral operator is the most prominent example of a
convolution operator with a piecewise continuous symbol. The Fredholm
theory of Toeplitz and Wiener-Hopf operators with continuous and
piecewise continuous (matrix) symbols is well presented in a series of
classical and recent monographs. Symbols beyond piecewise continuous
symbols have discontinuities of oscillating type. Such symbols emerge
very naturally. For example, difference operators are nothing but
convolution operators with almost periodic symbols: the operator defined
by (A