Simulik, V.M. (1997) “A theorem on the structure of a complete set of conformal-like series of conserved quantities for massless fields”,
Ukrains’kyi Matematychnyi Zhurnal, 49(12), pp. 1707–1711. Available at:
https://umj.imath.kiev.ua/index.php/umj/article/view/5177 (Accessed: 10 April 2025).