Yeah I am still getting errors when the answer is sorting and filtering correctly. This needs fixing.

You are not tackling the problem correctly.

The fact that the half of the length of the array equals the size of the set, doesn't mean that every number in the set occurs twice.

Any response on this one?

This should be a level 8 kata, don't you think?

I can not say too much. I can only say that this can be logically inferred. ;-)

See the comment of @micos7 above ^_^

Thanks for the clarification in the description, and also for the picture! Where did you find this drawing? :')

@micos7,
Thanks for your nice image ;-)
I've added it to kata's description.

I understood this bit but why can't there be a third case with A giving a wrong answer on purpose?
If A can't win, it is better for him to expect a tie rather than letting B win.
If no liar is allowed, then you should state it explicitely in the description ;-)

Can C see D? I don't understand how anyone but A could win? A is the only one who can see the most, wouldn't it be down to pure luck for another person to guess? Sorry, I don't understand?

Yeah, it looks like you're right. The dangers of only writing code to pass the tests, I guess.