Thanks! While you're here, is oconnore (https://news.ycombinator.com/item?id=9800705 )'s solution legal according to your rules?

EDIT: Also, the wording

> There's no way to read the values from the array, only to set them and compare them for equality

seems unchanged.

The preceding sentence was changed to be more explicit that the bullet points are about the "user-facing API" being unrealistic. They're not implementation rules/constraints.

I think his solution is a little bit tongue in cheek - it shows how much easier it is to solve using transactional memory compared to low-level concurrency primitives. So it cheats by using very powerful techniques instead of the very weak ones that the post says to use. You couldn't use his solution in C++ for instance, because C++ doesn't come with garbage collection or transactional memory.

I see; I don't know enough about concurrency to recognise the tongue-in-cheek-ness (or whatever). Thanks for explaining!