Yes, I realize that. However, the alternative using a variadic fixed point combinator looks slightly cleaner and would (optimally) reduce to the same term. For example, using a list-based vfix:

    even' _ odd n = if n == 0 then True else (odd (n - 1)))
    odd' even _ n = if n == 0 then False else (even (n - 1))
    even = head $ vfix [even', odd']
    odd = tail $ vfix [even', odd']

Here, the functions don't need to be passed explicitly to the "recursive" calls. I prefer this a lot, it makes my lambda functions much more readable.