mat( ( -1, 0, 0,  0, 1, 0, 0),
     (  2,-1, 0,  0, 0,-1, 0),
     (  0, 1,-1,  0, 0, 0, 0),
     (  0, 0, 1, -1, 0, 0,-1),
     (  0, 0, 0,3/5,-1, 0, 0),
     (  0, 1, 0,  0, 1, 0, 0),
     (  0,-1, 0,  0,-1, 0, 0),
     (  0, 0, 1,  0, 0, 0, 0 ) )