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

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

if (x->rtrb_link[1] == NULL)
  {
    x->rtrb_rtag = RTRB_THREAD;
    x->rtrb_link[1] = y;
  }
