A.
p↑.rlink↑.llink:=q;p↑.rlink:=q;q↑.llink:=p;q↑.rlink:=p↑,rlink;
B.
p↑.llink↑.rlink:=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↑.1link↑.rlink:=q;p↑.llink:=q;