Kiriyatzkii, E. G., and J. Kirjackis. “On Some Extremal Problems on Linearly Invariant Classes”. Nonlinear Analysis: Modelling and Control 10, no. 2 (April 25, 2005): 161–170. Accessed July 7, 2025. https://www.zurnalai.vu.lt/nonlinear-analysis/article/view/15130.