[1 0 0 0
 2 1 0 0
 3 4 1 0
 1 0 2 1 ] *
[2 -1  0  3
 0  1  1  2
 0  0  0 -2
 0  0  0  1 ]

[1 0 0 0
 2 1 0 0
 3 4 1 0
 1 0 2 1 ] *
[2 -1  0  3
 0  0  1  2
 0  0  0  0
 0  0  0  0 ]

[1 0 0 0
 2 1 0 0
 3 4 1 0
 1 0 2 1 ] *
[2 -1  0  3
 0  0  0  0
 0  0  0  0
 0  0  0  0 ]

[1 0 0 0
 2 1 0 0
 3 4 1 0
 1 0 2 1 ] *
[0 -1  0  3
 0  0  0  2
 0  0  0  0
 0  0  0  0 ]