Krylov–Bogolyubov theorem

The Krylov–Bogolyubov theorem, often associated with the works of Nikolai Krylov and Nikolai Bogolyubov, is a result in the theory of dynamical systems and statistical mechanics. It addresses the existence of invariant measures for certain classes of dynamical systems, particularly in the context of Hamiltonian systems and stochastic processes. In more technical terms, the theorem typically applies to systems that can be described by a flow in a finite-dimensional phase space.