matrix3x3Multiply :: (Typed a, Num a) => [Stream a] -> [Stream a] -> [Stream a]
matrix3x3Multiply (x11:x12:x13:y11:y12:y13:z11:z12:z13:[]) (x21:x22:x23:y21:y22:y23:z21:z22:z23:[]) =
  [ x11*x21 + x12*y21 + x13*z21, x11*x22 + x12*y22 + x13*z22, x11*x23 + x12*y23 + x13*z23,
    y11*x21 + y12*y21 + y13*z21, y11*x22 + y12*y22 + y13*z22, y11*x23 + y12*y23 + y13*z23,
    z11*x21 + z12*y21 + z13*z21, z11*x22 + z12*y22 + z13*z22, z11*x23 + z12*y23 + z13*z23
  ]