The concept of quasiaverages and spaces of states

The fundamental content of Bogolyubov's concept of quasiaverages is considered. The problem of the nonuniqueness in the choice of the state space of a macroscopic system is investigated in the example of the Ising model. The basic methods of quasiaveraging are discussed. The microscopic description of heterophase states using the concept of quasiaverages is considered.