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With regards to the "readability" vs "efficiency" thing, I'd agree that they don't have to be entirely at odds. In the version of my kd-tree posted here I do feel I sacrificed too much readability with the aim of gaining performance, but in the rewrite (here) I found that almost all of the readability I sacrificed in the earlier version was unnecessary. Really, a good number of things that you might think are not optimized turn out to be taken care of by the JIT, so you just need to worry about higher level aspects in most cases.