ABOUT ONE PROBLEM WITH AN OBLIQUE DERIVATIVE FOR A MIXED EQUATION.

The main goal of this work is to show that the correctness of the problem with an oblique derivative specified at a departure from the characteristic for a mixed parabolic-hyperbolic equation with a characteristic line of changing type significantly depends on the class in which the solution is sought and on the value of the polar angle formed by the vector field defining the oblique derivative and the abscissa axis at the beginning of the departure.