rotatez :: Double -> Matrix
rotatez r = (( c, -s,  0,  0),
             ( s,  c,  0,  0),
             ( 0,  0,  1,  0),
             ( 0,  0,  0,  1))
   where c = cos r
         s = sin r
rotatez :: Double -> Matrix
rotatez r = (( c, -s,  0,  0),
             ( s,  c,  0,  0),
             ( 0,  0,  1,  0),
             ( 0,  0,  0,  1))
   where c = cos r
         s = sin r
rotatez r = (( c, -s,  0,  0),
             ( s,  c,  0,  0),
             ( 0,  0,  1,  0),
             ( 0,  0,  0,  1))
   where c = cos r
         s = sin r