On the constructive characterization of threshold functions

In this paper, structure of the set of threshold functions and complexity problems are considered. The notion of a signature of threshold function is defined. It is shown that if threshold function essentially depends on all of its variables then signature of this function is unique. Set of threshold functions is partitioned onto classes with equal signatures. Theorem characterizing this partition is proved. Importance of the class of monotone threshold functions is emphasized. Complexity of transferring one threshold function specified by the linear form into another is examined. It is shown that in the worst case this transferring would take exponential time. Structure of the set of linear forms specifying the same threshold function is also examined. It is proved that for any threshold function this set of linear forms has unique basis in terms of the operation of addition of the linear forms. It is also shown that this basis is countable.