[ [ 1,-1,-1, 0,0,0, 0, 0 ],
  [ 0, 0, 1,-1,0,0, 0, 0 ],
  [ 0, 0, 0, 0,1,0,-1, 0 ],
  [ 0, 0, 0, 0,0,1, 0,-1 ] ]