TrukhanY., and SheremetaM. M. “Boundedness of the <em class="a-Plus-plus">l</Em&gt;-Index of the Naftalevich–Tsuji Product”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 56, no. 2, Feb. 2004, pp. 247-56, https://umj.imath.kiev.ua/index.php/umj/article/view/3748.