function link(state, prev, next) {
	if (prev === null) {
		state.first = next;
	} else {
		prev.next = next;
		prev.e.next = next && next.e;
	}

	if (next !== null) {
		next.prev = prev;
		next.e.prev = prev && prev.e;
	}
}
@param {EachState} state
@param {EachItem | null} prev
@param {EachItem | null} next