There is no need to attach anything. If you repaid it in 2017, the repayment will not affect your 2016 tax return. You will pay taxes on the full amount in 2016. When you file your 2017 tax return, then come back and we can help you with reporting the repayment.
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https://www.irs.gov/publications/p17/ch12.html#en_US_2016_publink1000172015">https://www.irs.gov/pub...>
