Okay, thank you for explanation!

It is probably due to the low satisfaction rate. Katas with low rating are automatically retired (I don't know exactly which are the conditions for retirement).

The low rating is the subjective appreciation of beta testers. The reason for the low rate is probably because the task was considered too basic to be interesting (there is already a number of katas implying basic OOP manipulations).

Can you explain why the kata is retired? I did my best in creating my first kata clean, after reading all the docs. What was my mistake?

Oh, this hint is really helpful! I think, it would be reasonable to throw exceptions when negative numbers are used.

Thank you very much! 👍

When the increasing method is fed with a negative input, the score may become negative. This is not handled correctly by the reference solution, which only enforces the non-negativity constraint for the decreasing method.