c 

1 4
# n   m   1
1 0   0   1
1
n m 

1 

1
4 6
#   i   j   n   m   1
1   1   0   0   0  -1
1  -1   0   1   0   0
1   0   1   0   0  -1
1   0  -1   0   1   0
0   0   0

0

1
2 8
#  c1  c2   i   j   n   m   1
0   1   0  -1  -1   0   0   0
0   0   1  -1   0   0   0   0
0