if (header.link_next != e) {
unchain(e);
chain(header, header.link_next, e);
if (header.link_prev != e) {
unchain(e);
chain(header.link_prev, header, e);
case FORCE_FIRST:
case FIRST:
chain(header, header.link_next, e);
break;
case FORCE_LAST:
case LAST:
chain(header.link_prev, header, e);
break;