BabenkoV. F., Gun’koM. S., and RudenkoA. A. 2014. “Optimal Recovery of <em class="a-Plus-plus">n</Em&gt;-Linear Functionals According to Linear Information”. Ukrains’kyi Matematychnyi Zhurnal 66 (7), 884–890. https://umj.imath.kiev.ua/index.php/umj/article/view/2186.