(dimacs f) is the pair (ps,vs) where ps is the set of formulas
wich corresponds to the formula in DIMACS format writed in the file f and
vs is the list of variables wich occurs in any propositional formula.
(formulas f) is the pair (ps,vs) where ps is the set of formulas
wich corresponds to the formula in Prover9 format writed in the file f and
vs is the list of variables wich occurs in any propositional formula.