Kopaliani, T. S. 2008. “Littlewood - Paley Theorem on $L^{p(t)}(\mathbb{R}^n)$ Spaces”. Ukrains’kyi Matematychnyi Zhurnal 60 (12), 1709 -. https://umj.imath.kiev.ua/index.php/umj/article/view/3283.