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A method for solving a quasilinear nonelliptical equation of the second order is developed and we give classification and parametrization of simple elements of the equation. The equation for potential stationary flow of a compressible gas in a supersonic region is considered as the first example of an application of the method . A new exact solution is obtained which may be treated as a nonlinear analogue of a stationary wave. A gauge structure for the equation and an analogue of the Baeklund transformation are introduced. Certain classes of exact solutions for an equation of a nonstationary potential flow of a compressible gas are found. This is the second example of an application of the method. Finally a physical analysis of the results is carried out.

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Marek (Wojciech) Kalinowski was born and educated in Poland .He obtained MS degree inphysics ,MS degree in mathematics and computer science ,MA degree in philosophy and PhD degree in physics. He created about 150 items ( books, papers,preprints, chapters,technical reports etc.) in physics,mathematics,philosophy and engineering.

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