Mel'nichenko, I. P., and S. A. Plaksa. 1995. “Reduction of the Principal Biharmonic Problem for a Quadrant to Nonsingular Integral Equations”. Ukrains’kyi Matematychnyi Zhurnal 47 (6): 775–784. https://umj.imath.kiev.ua/index.php/umj/article/view/5471.