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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 _merge_meta(left, right, result, clean=True):
 """Merge metadata from left and right onto results. This is used during class initialization. This should also be used by operators to merge metadata after creating a new instance but before returning it. Result's metadata is modified in-place. Parameters left, right : number, `BaseSpectrum`, or `~astropy.modeling.models` Inputs of an operation. result : `BaseSpectrum` Output spectrum object. clean : bool Remove ``'header'`` and ``'expr'`` entries from inputs. """

        # Copies are returned because they need some clean-up below.
        left = BaseSpectrum._get_meta(left)
        right = BaseSpectrum._get_meta(right)

        # Remove these from going into result to avoid mess.
        #   header = FITS header metadata
        #   expr = ASTROLIB PYSYNPHOT expression
        if clean:
            for key in ('header', 'expr'):
                for d in (left, right):
                    if key in d:
                        del d[key]

        mid = metadata.merge(left, right, metadata_conflicts='silent')
        result.meta = metadata.merge(result.meta, mid,
                                     metadata_conflicts='silent')