Check that a given arXiv ID is a valid one.

    :param arxiv_id: The arXiv ID to be checked.
    :returns: Boolean indicating whether the arXiv ID is valid or not.

    >>> is_valid('1506.06690')
    True

    >>> is_valid('1506.06690v1')
    True

    >>> is_valid('arXiv:1506.06690')
    True

    >>> is_valid('arXiv:1506.06690v1')
    True

    >>> is_valid('arxiv:1506.06690')
    True

    >>> is_valid('arxiv:1506.06690v1')
    True

    >>> is_valid('math.GT/0309136')
    True

    >>> is_valid('abcdf')
    False

    >>> is_valid('bar1506.06690foo')
    False

    >>> is_valid('mare.GG/0309136')
    False

def is_valid(arxiv_id):
    """
    Check that a given arXiv ID is a valid one.

    :param arxiv_id: The arXiv ID to be checked.
    :returns: Boolean indicating whether the arXiv ID is valid or not.

    >>> is_valid('1506.06690')
    True

    >>> is_valid('1506.06690v1')
    True

    >>> is_valid('arXiv:1506.06690')
    True

    >>> is_valid('arXiv:1506.06690v1')
    True

    >>> is_valid('arxiv:1506.06690')
    True

    >>> is_valid('arxiv:1506.06690v1')
    True

    >>> is_valid('math.GT/0309136')
    True

    >>> is_valid('abcdf')
    False

    >>> is_valid('bar1506.06690foo')
    False

    >>> is_valid('mare.GG/0309136')
    False
    """
    match = REGEX.match(arxiv_id)
    return  (match is not None) and (match.group(0) == arxiv_id)