(Vlad Spataru) Index the rows and columns from 0 to 100. We shall only work modulo 101 in what follows. Observe that we may let (0,0)=0 by adding some constant to all the terms of the table. Next, because of the condition in the statement,
(u,v)+(i,j)=(u,j)+(i,v),
for any u,v,i,j. Thus, there exist a0=0,a1,…,a100 and b0=0,b1,…,b100 so that (i,j)=ai+bj. Now, letting Σa and Σb be the sum of the ai and the bj respectively, the condition in the statement then yields Σa+Σb=0. Note that
i=0∑100x101bi=(i=1∑100xbi)101:=i=0∑∞xiα(i).
Observe that the number of ways of adequately choosing one cell from each row corresponds to the number of 101-tuples with values from {b0,b1,…,b100} with sum equal to Σb that is α(Σb)+α(101+Σb)+….
Using the fact that 101 is prime and computing the latter expression for x=exp(2πi/101) we get the desired
0=i=0∑∞α(101i+Σb).