Balder's well-known existence theorem (1983) for infinite-horizon optimal control problems is extended to the case when the integral functional is understood as an improper integral. Simultaneously, the condition of strong uniform integrability (over all admissible controls and trajectories) of the positive part max{f 0 , 0} of the utility function (integrand) f 0 is relaxed to the requirement that the integrals of f 0 over intervals [T, T ′ ] be uniformly bounded from above by a function ω(T, T ′ ) such that ω(T, T ′ ) → 0 as T, T ′ → ∞. This requirement was proposed by A.V. Dmitruk and N.V. Kuz'kina (2005); however, the proof in the present paper does not follow their scheme but is instead derived in a rather simple way from the auxiliary results of Balder himself. An illustrative example is also given.
MSC2010: 49J15, 49J45One of the most general and well-known results on the existence of solutions to infinitehorizon optimal control problems was proved by Balder [6]. Almost all conditions of his theorem are local in time (i.e., they must hold only at each separate instant of time or on each finite time interval) and ensure the existence of solutions to similar problems on finite time intervals. The only condition that regulates the behavior of the system at infinity is the requirement of strong uniform integrability of the positive part of the integrand in the objective functional over all admissible controls and corresponding trajectories. Later several authors achieved some progress in weakening this condition.The present paper also contributes to this direction. As an alternative to Balder's uniform integrability, we use the condition of "uniform boundedness of pieces of the objective functional" proposed by Dmitruk and Kuz'kina [10]. Note that they considered a significantly narrower class of optimal control problems, while for the general case only a scheme was outlined (without statement of particular results that can be obtained by following this scheme 1 ). So the present paper is in a sense a logical completion of the paper [10]. However, *