 The monotonic Boolean functions are precisely those that can be defined by an expression combining the inputs (which may appear more than once) using only the operators "and" and "or" (in particular "not" is forbidden).For instance "at least two of "a","b","c" hold" is a monotonic function of "a","b","c", since it can be written for instance as (("a" and "b") or ("a" and "c") or ("b" and "c")).The number of such functions on "n" variables is known as the Dedekind number of "n".