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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 _propagate_packages(self):
 r"""Propogate packages. Make sure that all the packages included in the previous containers are part of the full list of packages. """


        super()._propagate_packages()

        for item in (self.preamble):
            if isinstance(item, LatexObject):
                if isinstance(item, Container):
                    item._propagate_packages()
                for p in item.packages:
                    self.packages.add(p)