mat( (    1,   1, -1,   1, -1, 1,-1),
     ( -1/4,-1/4,1/4,   0,  0, 0, 0),
     (    0,   0,  0,-1/4,1/4, 0, 0),
     (    0,   0,  0,   0,  0,-1, 1),
     (    0,   0,  0,   0,  0, 1,-1 ) )