  Degenerate hyperbolic equations are dealing with many important issues for
applied nature. While a variety of degenerate equations and boundary
conditions, successfully matched to these differential equation, most in the
characteristic coordinates reduced to Euler-Darboux one. Some boundary value
problems, in particular Cauchy problem, for the specified equation demanded the
introduction of special classes in which formulae are simple and can be used to
meet the new challenges, including Delta-problems in squares that contain
singularity line for equation coefficients with data on adjacent or parallel
sides of the square. In this short communication the generalized Euler-Darboux
equation with negative parameters in the rectangular region is considered.
