General exact controllability results for dynamic systems with skew symmetric operators and behaviour at infinite time

The author has previously pointed out the specific property of exact controllability that linear dynamic systems with skew symmetric operators possess. This particular property holds for the wave equation. In the previous work, there was an assumption stated in terms of the controllability operator. To a certain extent, this assumption restricted the full extent of the abstract formalism that was used. In this paper, an attempt is made to eliminate this awkward assumption, and to express conditions only in terms of the operators A, B characterizing the system