  We discuss the notion of hidden correlations in classical and quantum
indivisible systems along with such characteristics of the correlations as the
mutual information and conditional information corresponding to the entropic
subadditivity condition and the entropic strong subadditivity condition. We
present an analog of the Bayes formula for systems without subsystems, study
entropic inequality for von Neumann entropy and Tsallis entropy of the
single-qudit state, and discuss the inequalities for qubit and qutrit states as
an example.
