[mrweasel]

I did not know that, and I question that choice as well. Why would you use that?

It's a little less bad, because you can just have your own style guide that says "Don't do that".

[steezeburger]

It's common math notation to have f and f prime to represent something derived from f.

[Degorath]

As an OCaml beginner I've mostly seen it used for inner functions in lieu of calling the inner function `f_impl`.