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Comment by billforsternz | Hacker News Reader

This video is really about the rarest Standard Algebraic Notation (SAN) corner cases, which is more than a little different from rarest moves. But the author basically acknowledges this, and 'rarest moves' is so hard to really define anyway. So kudos it's otherwise a great video.

I'm about equally impressed with the statistical analysis and the video construction and presentation. I can imagine tackling the former, but not the latter. I did notice a few mistakes in the video presentation though (eg a Bd4# that he presented as Be4#). I imagine at some point he just thought "I've polished this thing enough" and stopped.

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Rarest I think is pretty easy. It's just board state transition.

You'd probably need 15 orders more magnitude of data to get there, but the definition itself is pretty straight forward.

Thinking about it, one could also have a canonical state transition based on the game state transitions.(i.e. expand the game tree).

This would include not only the board state, but all the moves made up to reaching it.

It has a useful meaning for openings.

But it is so sparsely populated by actual games that "rarest" becomes too easy - many moves have been made only once under this definition.

You don't need to know anything before. Game theory has a word for this type of game called "perfect information"

https://en.m.wikipedia.org/wiki/Perfect_information

It might be interesting, but the previous board state should not be a relevant factor when considering rarest move

Board state itself becomes unique pretty quickly, so you would just end up with a gigantic lot of "moves" played only 1 time.

EDIT: so you could define "rare" moves as the biggest difference of occurrences between state N and state N+1.

I bet it becomes unique far far less often then most people think.

Computing the number of permutations is thoroughly unconvincing.

For instance, there's 20 possible first moves and of those only probably 2 are played 95% of the time. You can certainly compute what the rates open is and the rarest response that's actually played or the rarest response to the most common open

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