code: private boolean solve(final int lit) {
          this.assumptions.push(not(lit));
          final boolean sat = solve(null, this.assumptions) == Tristate.TRUE;
          this.assumptions.pop();
          return sat;
      }
docs: Tests the given literal with the formula on the solver for satisfiability.
  @param lit literal to test
  @return {@code true} if satisfiable, otherwise {@code false}