<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 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. True True True True True True True False False False """

    match = REGEX.match(arxiv_id)
    return  (match is not None) and (match.group(0) == arxiv_id)