def get_ISSNs(self):
invalid_issns = set(self.get_invalid_ISSNs())<EOL>return [<EOL>self._clean_isbn(issn)<EOL>for issn in self["<STR_LIT>"]<EOL>if self._clean_isbn(issn) not in invalid_issns<EOL>]<EOL>
Get list of VALID ISSNs (``022a``).

Returns:
    list: List with *valid* ISSN strings.