A.p↑.rlink↑.ll I nk:=q;p↑.rlink:=q;q↑.llink:=p;q↑.rlink:=p↑.rlink; B.p↑.llink↑.rl I nk:=q;p↑.llink:=q;q↑.rlink:=p;q↑.llink:=p↑.llink; C.q↑.llink:=p;q↑.rlink:=p↑.rlink;p↑.rlink ↑.llink:=q;p↑.rlink:=q; D.q↑.rlink:=p;q↑.llink:=P↑,llink;p↑.llink↑.rlink:=q;p↑.llink:=q;