  We describe a method of analytic evolution of distribution amplitudes (DA)
that have singularities, such as non-zero values at the end-points of the
support region, jumps at some points inside the support region and cusps. We
illustrate the method by applying it to the evolution of a flat (constant) DA,
antisymmetric flat DA and then use it for evolution of the two-photon
generalized distribution amplitude. Our approach has advantages over the
standard method of expansion in Gegenbauer polynomials, which requires infinite
number of terms in order to accurately reproduce functions in the vicinity of
singular points, and over a straightforward iteration of an initial
distribution with evolution kernel. The latter produces logarithmically
divergent terms at each iteration, while in our method the logarithmic
singularities are summed from the start, which immediately produces a
continuous curve, with only one or two iterations needed afterwards in order to
get rather precise results.
