def any_tagged_cell(nb, tag):
    """Whether the notebook contains at least one cell tagged ``tag``?

    Parameters
    ----------
    nb : nbformat.NotebookNode
        The notebook to introspect
    tag : str
        The tag to look for

    Returns
    -------
    bool
        Whether the notebook contains a cell tagged ``tag``?
    """
    return any([tag in cell.metadata.tags for cell in nb.cells])