@Daan (the other one) A min-heap only tells me the smallest integer in the set, not the smallest one not in the set. What you'd need is a max-heap of all the elements not in the set, but I'm afraid there are too many 64 bit integers to make this sufficient. That's what I meant by the "complement of a priority queue" above.

As for the markdown: Yep, that's known, but nobody bothered to fix it yet. As a workaround, you can percent-encode the parens in links.