Determine all pairs of positive integers (m,n) for which there exists a bijective function f:Zm×Zn→Zm×Znsuch that the vectors f(v)+v, as v runs through all of Zm×Zn, are pairwise distinct. (For any integers a and b, the vectors [a,b],[a+m,b] and [a,b+n] are treated as equal.)Poland, Wojciech Nadara number theoryfunctionRMMRMM 2020RMM Shortlist