x = pa[k - 2];
x->rtrb_color = RTRB_RED;
y->rtrb_color = RTRB_BLACK;

x->rtrb_link[0] = y->rtrb_link[1];
y->rtrb_link[1] = x;
pa[k - 3]->rtrb_link[da[k - 3]] = y;

if (y->rtrb_rtag == RTRB_THREAD)
  {
    y->rtrb_rtag = RTRB_CHILD;
    x->rtrb_link[0] = NULL;
  }
