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