Consider for example the boolean conjuctive normal form with 8 variables {a, b, c, d, e, f, g, h} and 5 clauses
(to the rigth of -sign are the negative literals and to the left the positive literals)
The corresponding text Boolean file consists of 6 words (one more than the clauses number) separated by the connective & (for disjunctive form the connective is +). The first 5 words describe the clauses; the last word (without -sign) gives (in one word) all the variables. Thus dummy variables (like f in the example) are keeped.
The given example has thus the text file structure
ab-e & g-abde & h-ag & -agh & bcd & abcdefgh