Muskhelishvili, N. I. Singular Integral Equations (Singulyarnye integral’nye uravneniya), 1946. In Russian.

Мусхелишвили Н. И.
Сингулярные интегральные уравнения. Граничные задачи теории функций и некоторые их приложения к математической физике.
Москва — Ленинград : Государственное издательство технико-теоретической литературы (Гостехиздат), 1946.
448 с. Твердый издательский переплет, обычный формат. Тираж 5000 экз.
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Muskhelishvili, Nikoloz (Niko) Ivanovich.
Singular Integral Equations. Boundary Value Problems in Function Theory and Some of Their Applications to Mathematical Physics.
Moscow — Leningrad : Gostekhizdat, 1946.
448 pp. Hardcover, standard format. 1st edition. Print run: 5,000 copies. In Russian.

This 1946 volume is a world-renowned masterpiece of 20th-century mathematics. Written by Nikoloz (Niko) Muskhelishvili (1891–1976), the founder and long-time President of the Georgian Academy of Sciences and a towering figure in the Soviet school of mechanics, this first edition represents the definitive formalization of the theory of singular integral equations. Published immediately after World War II by Gostekhizdat, the book played a crucial role in the post-war advancement of theoretical physics and engineering.
The monograph provides a systematic and exhaustive treatment of singular integral equations containing Cauchy-type kernels. Muskhelishvili’s primary achievement in this work was the application of the theory of functions of a complex variable to solve boundary value problems, particularly the Riemann–Hilbert problem. By transforming these complex problems into integral equations, he provided a powerful toolkit for addressing challenges in the theory of elasticity, hydrodynamics, and aerodynamics.