Malamud, M. M., and R. Zuidwijk. “Simultaneous Similarity of Pairs of Convolution Volterra Operators to Fractional Powers of the Operator of Integration”. Methods of Functional Analysis and Topology, vol. 9, no. 2, June 2003, pp. 154-62, https://zen.imath.kiev.ua/index.php/mfat/article/view/211.