The only Boolean functions accepted in this format are clauses.
A clause has the following syntax:
[-]<var> ... [-]<var> 0
where <var> is a variable and '-' in front of a <var> makes it a negative literal and no '-' in front of
<var> makes it a positive literal. There are no commas in
the variable list and the list is terminated with a 0. Variables
may appear in a variable list in any order and are separated by
blank characters. For an example see Figure 3,
Page
.