comp1 : List(N) -> List(N) -> List(N)
comp1 xs ys = [ x + y | x in xs, 2 divides x, y in ys, 2 divides y, x + y >= 50 ]

pythagTriples : List (N*N*N)
pythagTriples = [ (a,b,c)
  | a in [1 .. 20]
  , b in [1 .. 20]
  , c in [1 .. 20]
  , a^2 + b^2 == c^2
  ]