public void unlink() {
if (next != null) next.prev = prev;
if (prev != null) prev.next = next;
if (parent.child == this) parent.child = next;
if (parent.lchild == this) parent.lchild = prev;
next = null;
prev = null;
}
public void link() {
if (parent.lchild != null) parent.lchild.next = this;
if (parent.child == null) parent.child = this;
this.prev = parent.lchild;
parent.lchild = this;
}