1+r2+r3+r4
4 0 0 0
1 1 -1 -1
1 -1 1 -1
1 -1 -1 1
r1*(1/4),r2-r1,r3-r1,r4-r1
1 0 0 0
0 1 -1 -1
0 -1 1 -1
0 -1 -1 1
r3+r2,r4+r2
1 0 0 0
0 1 -1 -1
0 0 0 -2
0 0 -2 0
r3*(-1/2),r4*(-1/2),r2+r3+r4
1 0 0 0
0 1 0 0
0 0 0 1
0 0 1 0
r3r4
1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1