When you use an underscore in a name, make sure to escape it first, like so:

I suspect that formally the A\_p are one type of [hyperprior](http://en.wikipedia.org/wiki/Hyperprior), but not all hyperpriors are A\_p (a/k/a metaprobabilities).

(This is necessary because underscores are yet another way to make things italic, and only applies to comments, as posts use different formatting.)

Yeah - from what I've seen, something mathematically equivalent to A_p distributions are commonly used, but that's not what they're called.

Like, I think you might call the case in this problem "a Bernoulli random variable with an unknown parameter". (The Bernoulli random variable being 1 if it gives you $2, 0 if it gives you $0). And then the hyperprior would be the probability distribution of that parameter, I guess? I haven't really heard that word before.

ET Jaynes, of course, would never talk like this because the idea of a random quantity existing in the real world is a mind projection fallacy. Thus, no "random variables". So he uses the A_p distribution as a way of thinking about the same math without the idea of randomness. Jaynes's A_p in this case corresponds exactly to the more traditional "the parameter of the Bernoulli random variable is p".

(btw I have a purely mathematical question about the A_p distribution chapter, which I posted to the open thread: http://lesswrong.com/lw/ii6/open_thread_september_28_2013/9pbn if you know the answer I'd really appreciate it if you told me)