solver for quantified boolean formulae

 DepQBF is a search-based solver for quantified boolean formulae (QBF)
 in prenex conjunctive normal form. It is based on the DPLL algorithm
 for QBF, called QDPLL, with conflict-driven clause and solution-driven
 cube learning. By analyzing the syntactic structure of a formula,
 DepQBF tries to identify independent variables. In general, information
 on independent variables can be represented in the formal framework of
 dependency schemes. DepQBF computes the so-called "standard dependency
 scheme" of a given formula. In addition to other benefits, information
 on independent variables often increases the freedom for decision
 making and clause learning.