Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Polar coding has also proven to be a versatile coding method capable of achieving the information-theoretic limits in a wide range of source and channel coding problems; for a representative list of such work, we cite [2], [3], [4], [5], [6], [7].
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