I don't necessarily agree that this kata has to be upgraded to the harder form, though I do think that's very valuable info to disseminate. On a related note, I knew about DLists and how they work, but somehow never came across the ShowS type before – thanks for the tip!

It's not an issue of the kata but it seems to be a CW problem. See: https://github.com/Codewars/codewars.com/issues/379. You can complete the bug report.

You're right, my bad, 'y' has been added and the tests updated as such

No it shouldn't this is because for an empty list minimum is never evaluated as delete will handle the case of an empty list without touching it's first argument.