code: private GBSNode linearize(
      DeleteStack.Linearizer       xx,
      GBSNode       p)
    {
      xx.headp = null;
      xx.lastp = null;
      innerLinearize(xx, p);
      return xx.headp;
    }
docs: Turn a sub-fringe into a linear list.
  
  <p>If you look at the diagrams of insert fringe balancing in
  GBSInsertFringe you will observe that as a fringe grows on insert
  it starts out as a linear list and, when it reaches the right
  length, suddenly becomes a tree.  When a full fringe sub-tree has a
  node deleted, it reverts once more to being a linear list.</p>