שנים אדוקים בשטר (Bava Metzia 7a)

The Rishonim point out that this case shows that even by a ודאי רמאי you say יחלוקו. By שנים אדוקים בשטר one of them is definitely lying, he either paid off the loan or he didn't and yet the din is יחלוקו. However, the חלוקה can be אמת as it is possible that he paid off half the loan. This very much ties into a previous post Does everyone hold from the סברא of ודאי רמאי? (Bava Metzia 2a-3a)