View Compilation Error

0_0_31993121_8586.cpp: In function 'int Gauss(int, int)':
0_0_31993121_8586.cpp:48:47: error: 'k' was not declared in this scope
                     a[i][j]=(a[i][j]*ta%2 - a[k][j]*tb%2 + 2) % 2;
                                               ^