ON THE EXISTENCE OF PERIODIC SOLUTIONS OF SOME NONLINEAR PROBLEMS OF THERMAL CONTROL Статья Gurevich P.L., Eger V., Skubachevskiĭ A.L. Doklady Akademii Nauk. 2008.
A SIMPLE `FINITE APPROXIMATIONS' PROOFS OF THE PONTRYAGIN MAXIMUM PRINCIPLE UNDER REDUCED DIFFERENTIABILITY HYPOTHESES Статья Arutyunov Aram V., Vinter Richard B., Sumin Vladimir I. Set-Valued Analysis. Том 12. 2004. С. 5-24