User blog comment:Alemagno12/Divine Presence/@comment-1605058-20170201103530/@comment-30754445-20170201104211

R is also a function:

R(foo,5) = foofoofoofoofoo

It doesn't output a number, but it is definitely a function: R:(UxN)→U where "U" is the set of all unicode strings.

C and RO though, are not functions. Not in the way they are described in the text, anyway.