Rukasov, V. I. 2003. “Best <em class="a-Plus-plus">n</Em&gt;-Term Approximations in Spaces With Nonsymmetric Metric”. Ukrains’kyi Matematychnyi Zhurnal 55 (4), 500-509. https://umj.imath.kiev.ua/index.php/umj/article/view/3923.