code: protected int pickBranchLit() {
      int next = -1;
      while (next == -1 || this.vars.get(next).assignment() != Tristate.UNDEF || !this.vars.get(next).decision())
        if (this.orderHeap.empty())
          return -1;
        else
          next = this.orderHeap.removeMin();
      return mkLit(next, this.vars.get(next).polarity());
    }
docs: Picks the next branching literal.
  @return the literal or -1 if there are no unassigned literals left