Skrypnik, W.I. (2001) “On the Evolution Operator of the Gradient Diffusion Hierarchy for Plane Rotators”,
Ukrains’kyi Matematychnyi Zhurnal, 53(12), pp. 1664–1685. Available at:
https://umj.imath.kiev.ua/index.php/umj/article/view/4386 (Accessed: 10 April 2025).