Code Fragment: RBTree3

public:
  void removeElement(const Key& k)			// remove using key
      throw(NonexistentElementException) {
    BTPosition u = finder(k, T.root());			// find the node
    if (u.isNull())					// not found?
      throw NonexistentElementException("Remove nonexistent element");
    BTPosition r = remover(u);				// remove u
    if (T.isRoot(r) || isRed(r) || wasParentRed(r))
      setBlack(r);					// fix by color change
    else 						// r, parent both black
      remedyDoubleBlack(r);				// fix double-black r
  }
protected:
  void remedyDoubleBlack(const BTPosition& r) {		// fix double-black r
    BTPosition x, y, z;
    x = T.parent(r);
    y = T.sibling(r);
    if (isBlack(y))  {
      if (hasRedChild(y))  {				// Case 1: restructuring
        z = redChild(y);
        Color oldColor = color(x);			// save top vertex color
        z = T.restructure(z);				// restructure x,y,z
        setColor(z, oldColor);       setBlack(r);	// fix colors
        setBlack(T.leftChild(z));    setBlack(T.rightChild(z));
      }
      else {						// Case 2: recoloring
        setBlack(r); setRed(y);				// r=black, y=red
        if (isBlack(x) && !T.isRoot(x))
  	remedyDoubleBlack(x);				// fix double-black x
        setBlack(x);
      }
    }
    else {						// Case 3: adjustment
      if (y == T.rightChild(x))	  z = T.rightChild(y);	// z is the grandchild
      else 			  z = T.leftChild(y);	// ...on same side as y
      T.restructure(z);					// restructure x,y,z
      setBlack(y); setRed(x);				// y=black, x=red
      remedyDoubleBlack(r);				// fix by Case 1 or 2
    }
  }