def _before(node, values, positions, places=False):
    """
    Returns the set of all nodes that are before the given node.
    """
    n = node[positions['_n']]
    if places is not False:
        try:
            return [values[n - places]]
        except IndexError:
            return list()
    i = node[positions['i']]
    return values[n + 1 - i:n]
