def unregister_option(self, key, subkey):
if not self.open:<EOL><INDENT>return<EOL><DEDENT>key, subkey = _lower_keys(key, subkey)<EOL>_entry_must_exist(self.gc, key, subkey)<EOL>self.gc = self.gc[~((self.gc['<STR_LIT>'] == key) &<EOL>(self.gc['<STR_LIT>'] == subkey))]<EOL>
Removes an option from the manager.

        :param str key: First identifier of the option.
        :param str subkey: Second identifier of the option.

        raise:
            :NotRegisteredError: If ``key`` or ``subkey`` do not define
                any option.