TL;DR: Look at the lambda calculus definition of church_pow - (ce cb) f x.
Functions inside brackets are composed ; functions on the outside are just parameters for the previous function.
You can translate this definition into this resulting call ce(cb)(f)(x).
You can leave out each parameter that is not included inside brackets.
The same goes for church_mul: c1 (c2 f) x becomes c1(c2(f))(x), meaning you can leave out the x.

Hi - as someone who also discovered this area recently and who found it really interesting, I can highly recommend the following 2 videos that were linked to me in the Codewars Discord:

https://www.youtube.com/watch?v=3VQ382QG-y4

and

https://www.youtube.com/watch?v=pAnLQ9jwN-E

They use JavaScript rather than Python but it's very understandable.

Why were you able to leave out (f)(x) on church_pow and it still worked? Still trying to fully wrap my head around this concept, thx.

Good point .

You don't need "and len(n)". ;-)

Seriously, /? Is this Python2? :-o

Guido hates the return type being dependent on argument values. That's why even 8/2 is 4.0 in sane Pythons, not 4. Although, of course, there is an exception. Can you tell what it is? :-]

when add ocaml?

Python3 - great! Now can you please enable it for all katas that specify Python2? :-)