Javier F. Rosenblueth, Niels H. Wacher, The condition of Clebsch for mixed constrained optimal control problems, Vol. 2026 (2026), No. 3, pp. 1-13
N.U. Ahmed, Compact sets in the space of bounded linear operators and applications to optimal feedback control, Vol. 2026 (2026), No. 1, pp. 1-13