Consider a d x d table A, with d ≥ 1, where each of its entries contains exactly one element of the set {0, 1, 2}. Index the rows of the table starting from 0 for the top row, and the columns of the table starting from 0 from the left column. Hence, each element of the table is referenced by A_{i,j}, where i is the index of the row the element belongs in, and j is the index of the column the element belongs in. Furthermore, consider the sums of the entries of the table per row (namely R_i = ∑_{k=0}^{d-1} A_{i,k} for i = 0, 1, ..., d - 1), the sums of the entries of the table per column (namely C_j = ∑_{k=0}^{d-1} A_{k,j} for j = 0, 1, ..., d - 1) and the sums across the diagonals of the table (namely D_1 = ∑_{k=0}^{d-1} A_{k,k} and D_2 = ∑_{k=0}^{d-1} A_{k,d-1-k}). Show that there are always two sums (out the row, column and diagonal sums described above) that are equal.