LLRB RInsert

    Node * RInsert(Node* nptr, const T& tval)
    {
      if (nptr == 0) // insert new node a bottom
      {
	return NewNode(tval, RED);
      }
      // enforce Height Limiting Property on way down
      if (nptr->lchild_ && nptr->lchild_->IsRed())
	if (nptr->lchild_->lchild_ && nptr->lchild_->lchild_->IsRed())
	{
	  nptr = RotateRight(nptr);
	  nptr->lchild_->SetBlack();
	}
      if (pred_(tval,nptr->value_))       // go left
      {
	nptr->lchild_ = RInsert(nptr->lchild_, tval);
      }
      else if (pred_(nptr->value_,tval))  // go right
      {
	nptr->rchild_ = RInsert(nptr->rchild_, tval);
      }
      else                                // found
      {
	nptr->value_ = tval;
      }
      // enforce Left-Leaning Property on way up
      if (nptr->rchild_ && nptr->rchild_->IsRed())
      {
	nptr = RotateLeft(nptr);
	if (nptr->lchild_->IsBlack()) 
	{
	  nptr->SetBlack();
	  nptr->lchild_->SetRed();
	}
      }
      return nptr;
    }