This is somewhat in between interesting and strange (a lot of guessing, as by me and it looks like that it is not only by me ;-)). But after all managed.

Nice kata for those who like Linear Algebra and FP ^_^

Heh, it's interesting kata (I am not fully agree that it's 4 kyu, IMHO it's much easier than that). The description is done by Yoda, but it is like in the real life - most of the chances that understanding what those Yodas wrote you will take much more time than doing. Also, I've seen the solutions, so the question is why are those lambdas static? What's a point? Nevertheless, it's a nice kata but requires some description rewriting.

First, I really enjoyed this kata.

However, there is a pattern in test cases: inner brackets are round, then square and most outer are curly. (At least for Python) most clever solution won't pass if all brackets will be of the same type (you can check it). Either the description should be more verbose or test cases should include same type of brackets...