BabenkoV. F., KofanovV. A., and PichugovS. A. 2004. “Approximation of Sine-Shaped Functions by Constants in the Spaces $L_p,\; P < 1$”. Ukrains’kyi Matematychnyi Zhurnal 56 (6), 745–762. https://umj.imath.kiev.ua/index.php/umj/article/view/3795.