The positively closed classes of multivalued logic are characterised with the use of endomorphism semigroups. All subsemigroups of the symmetric semigroup of degree k are described which are semigroups of endomorphisms of positively closed classes in P k . On the base of the obtained results, we find all positively precomplete classes in P k .Prominent among a number of ways to classify the functions of multivalued logic are those based on the closure operators. On the set P k of the functions of k-valued logic, some operator O is defined; then the sets of functions in P k closed with respect to the operator O (usually referred to as the O-closed classes) form the O-classification of the set P k .The most known classification of such a kind is the classification based on the superposition operator. This classification has long been in use. But there exists an objective difficulty in its use: for any k 3 the number of closed classes in P k is continual (see [10]). In this connection, a great body of 'strong' closure operators have been introduced which for any k induce either finite or countable classifications on the set P k .One of the first strong closure operators is the parametric closure operator introduced by Kuznetsov in [3]. All twenty five parametrically closed classes of Boolean functions are found in [3] (see also [5]); the finiteness of the number of parametrically closed classes in P 3 is proved in [2], and for P k with k 4 it is established in [11]. It is worth noticing that for k 3 there is no complete description of parametrically closed classes in P k yet.Later, a more formalised definition of the parametric closure operator from the logic function viewpoint has been suggested in [4] (see also [5]). This definition permits to introduce more new strong closure operators. The first of them is the positive closure operator (which is even more strong than the parametric closure operator). The