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