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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 lipid_box(self):
 """The box containing all of the lipids. """

        if self._lipid_box:
            return self._lipid_box
        else:
            self._lipid_box = self.lipid_components.boundingbox
            # Add buffer around lipid box.
            self._lipid_box.mins -= np.array([0.5*np.sqrt(self.apl),
                                              0.5*np.sqrt(self.apl),
                                              0.5*np.sqrt(self.apl)])
            self._lipid_box.maxs += np.array([0.5*np.sqrt(self.apl),
                                              0.5*np.sqrt(self.apl),
                                              0.5*np.sqrt(self.apl)])
            return self._lipid_box