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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 issubset(self, other):
 """ Check if the contents of `self` is a subset of the contents of `other.` Args: other (:class:`FrameSet`):
 Returns: bool: :class:`NotImplemented`: if `other` fails to convert to a :class:`FrameSet` """

        other = self._cast_to_frameset(other)
        if other is NotImplemented:
            return NotImplemented
        return self.items <= other.items