VakarchukS. B. 1996. “On Exact Order Estimates of <em class="a-Plus-plus">N</Em&gt;-Widths of Classes of Functions Analytic in a Simply Connected Domain”. Ukrains’kyi Matematychnyi Zhurnal 48 (4), 543-47. https://umj.imath.kiev.ua/index.php/umj/article/view/5318.