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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 is_erc20(self):
 """ Check if the contract is an erc20 token Note: it does not check for correct return values Returns: bool """

        full_names = [f.full_name for f in self.functions]
        return 'transfer(address,uint256)' in full_names and\
               'transferFrom(address,address,uint256)' in full_names and\
               'approve(address,uint256)' in full_names