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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 get_main_chain_layers(self):
 """Return a list of layer IDs in the main chain."""

        main_chain = self.get_main_chain()
        ret = []
        for u in main_chain:
            for v, layer_id in self.adj_list[u]:
                if v in main_chain and u in main_chain:
                    ret.append(layer_id)
        return ret