| Summary: | The solvability issues of counterpart Holmgren’s boundary value problem with mixed conditions for a degenerate four-dimensional second-order Gellerstedt equation <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>H</mi><mfenced><mi>u</mi></mfenced><mo>≡</mo><msup><mi>y</mi><mi>m</mi></msup><msup><mi>z</mi><mi>k</mi></msup><msup><mi>t</mi><mi>l</mi></msup><msub><mi>u</mi><mrow><mi>x</mi><mi>x</mi></mrow></msub><mo>+</mo><msup><mi>x</mi><mi>n</mi></msup><msup><mi>z</mi><mi>k</mi></msup><msup><mi>t</mi><mi>l</mi></msup><msub><mi>u</mi><mrow><mi>y</mi><mi>y</mi></mrow></msub><mo>+</mo><msup><mi>x</mi><mi>n</mi></msup><msup><mi>y</mi><mi>m</mi></msup><msup><mi>t</mi><mi>l</mi></msup><msub><mi>u</mi><mrow><mi>z</mi><mi>z</mi></mrow></msub><mo>+</mo><msup><mi>x</mi><mi>n</mi></msup><msup><mi>y</mi><mi>m</mi></msup><msup><mi>z</mi><mi>k</mi></msup><msub><mi>u</mi><mrow><mi>t</mi><mi>t</mi></mrow></msub><mo>=</mo><mn>0</mn><mo>,</mo><mo> </mo></mrow></semantics></math></inline-formula><inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>m</mi><mo>,</mo><mi>n</mi><mo>,</mo><mi>k</mi><mo>,</mo><mi>l</mi><mo>≡</mo><mi>c</mi><mi>o</mi><mi>n</mi><mi>s</mi><mi>t</mi><mo>></mo><mn>0</mn><mo>,</mo></mrow></semantics></math></inline-formula> are studied in the finite domain <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mi>R</mi><mn>4</mn><mo>+</mo></msubsup></mrow></semantics></math></inline-formula>, where the values of normal derivatives are set on the piecewise smooth part of the boundary and the values of the desired function are set on the remaining part of the boundary. The main results of the work are the proof of the uniqueness of the considered problem solution by using an energy integral’s method and the construction of the solution of counterpart Holmgren’s boundary value problem in explicit form by means of Green’s function method, containing the hypergeometric Lauricella’s function <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mi>F</mi><mi>A</mi><mrow><mfenced><mn>4</mn></mfenced></mrow></msubsup></mrow></semantics></math></inline-formula>. Using the corresponding fundamental solution for the considered generalized Gellerstedt equation of elliptic type, we construct Green’s function. In addition, formulas of differentiation, some adjacent relations, decomposition formulas, and various properties of Lauricella’s hypergeometric functions were used to establish the main results for the aforementioned problem.
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