  The quasidistributions corresponding to the diagonal representation of
quantum states are discussed within the framework of operator-symbol
construction. The tomographic-probability distribution describing the quantum
state in the probability representation of quantum mechanics is reviewed. The
connection of the diagonal and probability representations is discussed. The
superposition rule is considered in terms of the density-operator symbols. The
separability and entanglement properties of multipartite quantum systems are
formulated as the properties of the density-operator symbols of the system
states.
