Demkiv, I. I., and V. L. Makarov. 2012. “Approximation of Urysohn Operator With Operator Polynomials of Stancu Type”. Ukrains’kyi Matematychnyi Zhurnal 64 (3), 318-43. https://umj.imath.kiev.ua/index.php/umj/article/view/2579.