Ice
Pedantic nitpick, but I might as well bring it up first so we can have it out of the way:<p>“There’s also an uncountable infinity of other patterns that all give you equally dense packings.”<p>According to the author’s examples using only {a, b, c}, the set of possible packings would be countably infinite.<p>Unfortunately, the article has kind of a breathless tone because it tries to cover quite a bit of ground all at once. Perhaps it’d’ve been better broken up, but it was still an interesting read. I’d never really considered that there must be different crystal structures to ice, though it seems perfectly obvious once explained.