where the entries in the columns labeled "r" and "c" denote the row and column of a position in a square and the rest of the row for fixed "r" and "c" values is filled with the entry in that position in each of the Latin squares. This process is reversible; given an OA(,) with ≥ 3, choose any two columns to play the "r" and "c" roles and then fill out the Latin squares with the entries in the remaining columns.