In honor of !!con, I was trying to think of programming-relevant uses of double exclamation marks. Other than denoting the end of a particularly funny programming joke (for example, a mangled homage to a famous paper), it seemed the best place to look might be in the world of double factorials. As it turns out, that wasn't as fruitful as I'd hoped, but I learned something interesting on the way to finding that out, and here it is.

TL;DR

You can learn interesting things about the order of complexity of an algorithm without knowing anything about how it works …

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