On minimal modulo 2 sums of products for switching functions

The minimal number of terms required for representing any switching function as a modulo-2 sums of products is investigated, and algorithm for obtaining economical realizations is described. The main result is the following: Every symmetric function of 2m+1 variables has a modulo-2 sum of products realization with at most 3m terms, but there are functions of n variables which require at least 2n/n long23 terms, for sufficiently large n.