The set of functions of many-valued logic is proposed to be classified with respect to two operations: superposition and transition to dual functions (the ^-classification). The contensive description of all 5-closed classes, which was begun by the author in 1979-82, was completed by Nguen Van Hoa. If fc > 5, then the set of functions of /:-valued logic has only two 5-precomplete classes: the class h of idempotent functions and the Slupecki class SLPk. In this paper the key properties determining the 5-closed classes are found and formalized in the form of the so-called basic relations. Using the Galois theory for Post algebras, it is shown that every 5-closed class of functions, which is not contained in SLPk, can be described by the basic relations. In the set of all systems of the basic relations all independent systems are determined which correspond to all 5-closed classes not contained in SLPk. An exact formula for the number of 5-closed classes contained in Ik is obtained which is a cubic polynomial in k.Let P k be the set of all functions of ^-valued logic [1,2]. Any analysis of functions of many-valued logic is necessarily based on structuring (classification) of subsets of P k . In discrete mathematics the approach based on generative capabilities of functions with respect to superposition has got the most prevalence for classification of subsets of P k . For k = 2 this approach gives the well-known countable Post classification [3,4]. For k > 3 the continuity of arising closed classes [5] is an objective obstacle for constructing and effective using of a similar classification. It compels to seek other, wider, closure operators which would include superposition and permit to avoid familiar undesirable effects.In the papers [6-10] the classifications of functions of many-valued logic self-dual with respect to permutations of the symmetric group and of the alternating group were constructed. The ideas underlying these classifications can be transferred from individual functions to classes of functions. More precisely, operations giving dual functions for permutations of a fixed group should be added to superposition. Above all, it is natural to consider the largest permutation group, that is, the symmetric group, which under this approach leads to the largest closed classes and, therefore, to the least number of closed classes. Several names were offered for the corresponding closed classes and the classification; we call them the 5-closed classes and the 5-classification respectively.