> let pred = \n. n shift (pair 0 err) snd in
> ...
- > Here is another solution, due to Martin Bunder and F. Urbanek:
+ > Here is another solution, that is attributed variously to Martin Bunder and F. Urbanek, or J. Velmans:
> let box = \a. \v. v a in
> let pred = \n. \s z. n (\b. box (b s)) (K z) I in