This is neat, but I can't believe the author managed to get through that entire explanation without ever using the word "heap". Perhaps he doesn't realise that

This is neat, but I can't believe the author managed to get through that entire explanation without ever using the word "heap". Perhaps he doesn't realise that his numbering is essentially using the same trick that we use with heaps to implement them within arrays? That doesn't mean it isn't nifty, of course.