Just to be clear, that is not the typo that I was referring to. The sentence I quoted should read "X&Y cannot be more probable than X...". But maybe the mistake is in the source?
Oh yeah, good catch. I wasn't actually reading the sentence before. :)
It's wrong in the original text. I've contacted the author, and corrected it (in brackets) in the LW post.
The chapter on judgment under uncertainty in the (excellent) new Oxford Handbook of Cognitive Psychology has a handy little section on recent critiques of the "heuristics and biases" tradition. It also discusses problems with the somewhat-competing "fast and frugal heuristics" school of thought, but for now let me just quote the section on heuristics and biases (pp. 608-609):
My thanks to MIRI intern Stephen Barnes for transcribing this text.