cat3 :: [Integer]
cat3 = map c [0 ..]
 where
  c n | n <= 0    = 1
      | otherwise = binom (2 * n) n - binom (2 * n) (n + 1)
cat3 :: [Integer]
cat3 = map c [0 ..]
 where
  c n | n <= 0    = 1
      | otherwise = binom (2 * n) n - binom (2 * n) (n + 1)
cat3 = map c [0 ..]
 where
  c n | n <= 0    = 1
      | otherwise = binom (2 * n) n - binom (2 * n) (n + 1)