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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def is_valid(doi):
 """ Check that a given DOI is a valid canonical DOI. :param doi: The DOI to be checked. :returns: Boolean indicating whether the DOI is valid or not. True True True True True True True False """

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