2 -1 1 0
0 -1 -1 -2
1 0 0 -1
1 1 0 -1
r1-2r3,r4-r3
0 -1 1 2
0 -1 -1 -2
1 0 0 -1
0 1 0 0
r1+r4,r2+r4
0 0 1 2
0 0 -1 -2
1 0 0 -1
0 1 0 0
r2+r1
0 0 1 2
0 0 0 0
1 0 0 -1
0 1 0 0
r(A)=3
2 -1 1 0
0 -1 -1 -2
1 0 0 -1
1 1 0 -1
r1-2r3,r4-r3
0 -1 1 2
0 -1 -1 -2
1 0 0 -1
0 1 0 0
r1+r4,r2+r4
0 0 1 2
0 0 -1 -2
1 0 0 -1
0 1 0 0
r2+r1
0 0 1 2
0 0 0 0
1 0 0 -1
0 1 0 0
r(A)=3