Über die partielle Differentialgleichung $$f(x,y)\frac{{\partial z}}{{\partial x}} + g(x,y)\frac{{\partial z}}{{\partial x}} = h (x,y).$$ II

Mathematische Zeitschrift -     

Über die Existenz von Integralen der partiellen Differentialgleichung $$f(x,y)\frac{{\partial z}}{{\partial x}} + g(x,y)\frac{{\partial z}}{{\partial x}} = 0$$ in der Umgebung eines singulären Punktes

Mathematische Zeitschrift -     

Some problems of the approximation of functions by “hyperbolic” Fourier-Hermite sums in the space L_2 \left( {{\mathbb{R}}^2 ,e^{ - x^2 - y^2 } } \right)

We obtain, among others, an exact estimate of the deviation of the “hyperbolic” Fourier-Hermite sums of the functions in the class L ₂ ^r (D) of the space indicated in the title.