docs: public void push(
      int         state,
      GBSNode     node)
    {
        _cidx++; _idx = _cidx;
        if (_cidx > GBSTree.maxDepth)
          throw new OptimisticDepthException(
            "maxDepth (" + GBSTree.maxDepth +
                     ") exceeded.  Depth is " + _cidx + ".");
  //    _idx++;
  //    _cidx = _idx;
  //    _endIndex = _idx;
      _state[_cidx] = state;
      _node[_cidx]  = node;
      if (index() > _maxIdx)
        _maxIdx = index();
    }