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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 as_bel(self) -> str: """Return this fragment variant as a BEL string."""

        res = '"{}"'.format(self.range)

        if FRAGMENT_DESCRIPTION in self:
            res += ', "{}"'.format(self[FRAGMENT_DESCRIPTION])

        return 'frag({})'.format(res)