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