Good catch! I’ve now added a reference implementation of mod_power inside the test suite to avoid this error.
This internal function is only used to compute expected results and won’t affect user solutions.

Fixed.

how could i fix that

Thank you for the feedback and sorry for the Kyu confusion, started playing with it and it seems like i ended up putting 1kyu instead of 5. I've made the modifications you suggested to the Kata.

Checked, it does not and did not at the moment the issue was opened.

if you use a recursive solution, double check the ref solution is not calling the user's one.

Because I couldnt reproduce the issue, I will close it to allow more people to see my kata and to see is there actually a problem, then, if there is, someone, perhaps you, can open a new issue.

I just tested your solution and it passes multiple times in a row, maybe you did something to cause this?

now actually fixed

Reproduces the issue, fixed.

Should be up now

Thanks for the feedback. I agree with returning None rather than False and I implemented random tests.

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In these cases, the barrels must be positioned in the last 2 positions on the list, as this is the smallest available space in which they fit. I think this is not clear in the description?

Ah, I modified the tests, the lists were being passed incorrectly, there was a possibility that they were modified and the tests could be bypassed. I made a copy of the lists so that the user cannot change them.