The code in my post is not intended to be a solution, 1nickt, as it is functionally no different from that in the OP. It's an example of debugging/diagnosing the problem and is intended to set Maire on the path. Your question here is precisely what I was hoping that Maire would ask.

In reply to Re^3: print lines which are not reverse duplicates by hippo
in thread print lines which are not reverse duplicates by Maire

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