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↑.llink↑.rlink := q; p↑.llink := q;