w->prb_color = PRB_BLACK;
f->prb_color = PRB_RED;

f->prb_link[1] = w->prb_link[0];
w->prb_link[0] = f;
g->prb_link[g->prb_link[0] != f] = w;

w->prb_parent = f->prb_parent;
f->prb_parent = w;

g = w;
w = f->prb_link[1];

w->prb_parent = f;
