void remove() {
sl.size--;
if (sl.first == this) sl.first = next;
else prev.next = next;
if (sl.last == this) sl.last = prev;
else next.prev = prev;
}
StateListNode(State q, StateList sl) {
this.q = q;
this.sl = sl;
if (sl.size++ == 0) sl.first = sl.last = this;
else {
sl.last.next = this;
prev = sl.last;
sl.last = this;
}
}
