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