Both katas have their differences. In mine you have to shift both upper and lowercase, and you have to do two distinct predicates for ciphering and unciphering. In the other you have to do a single multi-puropse predicate. Personally, I feel that mine is easier for starting, a bit of an excuse to learn the string_codes predicate, but the other is quite interesting too.

I feel like both katas are distinct enough to not be called duplicates, even if you can tweak the other solution to solve mine easily. I'll mark the issue as resolved, but you can comment again if you are not convinced by my argument.

For those doing this kata in Prolog, do NOT use the transpose in

:- use_module(library(clpfd)).

It gives problems with the tests for some reason, implement your own transpose