def find_node(nodes, *values):
    """Find the node having all of the search values.

    Parameters
    ----------
    nodes : dict
        each key is a node name
        each value is a 2-tuple containing
        up to two values flowing through
        the node
    values : *args
        every value in values must be in the 
        returned node

    Returns
    -------
    node : dict
        one-element dictionary of the form
        { node_name: search_values }
        representing the node found
        or None if no such node exists
    """
    search_vals= tuple(sorted(values))
    for node_name, node_vals in nodes.items():
        if search_vals == tuple(sorted(node_vals)):
            return {node_name: node_vals}
    return None