mat( (  0, 0, 0, 0,-1, 1, 0, 0, 0, 0,-1, 1,-1, 1),
     ( -2, 2, 0, 0, 1,-1, 0, 0, 0, 0, 0, 0, 0, 0),
     (  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
     (  1,-1, 0, 0, 0, 0, 0, 0,-1, 1, 0, 0, 0, 0),
     (  0, 0, 0, 0, 0, 0, 1,-1, 1,-1, 0, 0, 0, 0),
     (  0, 0, 1,-1, 0, 0, 0, 0, 0, 0, 1,-1, 1,-1),
     (  0, 0,-1, 1, 0, 0,-2, 2, 0, 0, 0, 0, 0, 0),
     (  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
     (  0, 0, 0, 0, 1,-1, 0, 0, 0, 0, 0, 0, 0, 0 ) )