Obukhovskiĭ, V., P. Zecca, and V. G. Zvyagin. “Optimal Feedback Control in the Problem of the Motion of a Viscoelastic Fluid”. Topological Methods in Nonlinear Analysis, vol. 23, no. 2, June 2004, pp. 323-37, https://apcz.umk.pl/TMNA/article/view/TMNA.2004.014.