ZhyhalloK. M., and ZhyhalloT. V. 2019. “On the Approximation of Functions from the Hölder Class given on a Segment by Their Biharmonic Poisson Operators”. Ukrains’kyi Matematychnyi Zhurnal 71 (7), 915-21. https://umj.imath.kiev.ua/index.php/umj/article/view/1485.