7 ms·

"Pawns may not be promoted to bishops;" ?????????? For real, I would absolutely love to know why that constraint was needed. Does anyone have info on why?

deleted 2y ago
[deleted]
abricq 2y ago
This rule is required because "as in chess", a pawn may promote to bishop. If you only remove the bishops from the starting position, then the rules of chess still allow bishops to come in later in the game (through a promotion). I am assuming they did not have enough memory to hold the rules of bishops, and therefore decided to completely remove them from the set of possible pieces. They allow rooks and knights promotion because these pieces are in the set of initial pieces: their rules are already implemented.
- csmeyer 2y ago
  Oh duh... well my question was not insightful but yes your answer makes sense, there are no bishops on the board lol
billforsternz 2y ago
I don't know why you've put lots of question marks, surely this is completely understandable. The whole point of this was that real chess was too big and complex, hence this dramatically smaller simpler version. There's no bishops in the start position so there's absolutely no way they'd bother implementing the bishop underpromotion corner case. Amusingly enough Rybka, the top engine for many years comparatively recently didn't implement bishop underpromotion either. For a much different reason. The programmer chose a not so great low level bit representation convention that forbid representing this case. He refused to fix the error because it would be too much work for the more-or-less non-existent situations where promoting to a bishop is the best move.
- teo_zero 2y ago
  Interesting. Does anybody have any example where a promotion to bishop would be preferable to Queen?
  - Sesse__ 2y ago
    Basically anything where a bishop would win, but a queen would put the other side in stalemate. For an extreme example, see https://en.wikipedia.org/wiki/Babson_task https://en.wikipedia.org/wiki/Babson_task.
  - rdlw 2y ago
    An example from a real GM game: https://youtu.be/CBoS9hSM6oM https://youtu.be/CBoS9hSM6oM
  - deleted 2y ago
    [deleted]
  - billforsternz 2y ago
    I'm at work so I'm not going to try and do some experiments, but my guess at relative frequency of (under)promotion being the best move (Queen = 1) is something like; Knight 1e-3 Rook 1e-5 Bishop 1e-7 A complicating factor in measuring this is that often a rook serves just as well as a queen, the opponent is going to capture immediately anyway, so players sometimes underpromote to a rook just for the fun factor. My number is more meant to represent cases where underpromotion really is the best move. Knight underpromotion is by far the most important, because a knight can do things a Queen can't, most typically give check to keep a combination going without giving the opponent an opportunity to play an active move. Rook and Bishop underpromotions can only be advantageous when they simultaneously avoid stalemate and keep a winning advantage. This is much more likely with a rook, for example in the famous Saavedra position, perhaps the most famous chess problem of all (it featured as decoration on our wedding cake :).
  - seanhunter 2y ago
    It is extremely rare. I saw an example involving Fabiano Caruana(current world #2)[1] and he was visibly excited in the post-match interview and said that's the first time in his whole career (which is thousands and possibly tens of thousands of games especially if you consider online etc) that he had done it. Edit to add: Here's the game. It was Caruana vs Robson 2021 and occurred in the 7th round of the USCF championship. Fabi's final move was to promote to bishop at which point Ray Robson resigned https://lichess.org/study/embed/iLDop9iy/wCdsPJJI https://lichess.org/study/embed/iLDop9iy/wCdsPJJI He did it for style points- a queen would have been just fine in that position. [1] https://youtu.be/Bz-V5wms0pk https://youtu.be/Bz-V5wms0pk
seanhunter 2y ago
Because they modelled the game with no bishops. You don't start with bishops and you also can't promote to a bishop.

deleted 2y ago

[deleted]

abricq 2y ago

This rule is required because "as in chess", a pawn may promote to bishop. If you only remove the bishops from the starting position, then the rules of chess still allow bishops to come in later in the game (through a promotion). I am assuming they did not have enough memory to hold the rules of bishops, and therefore decided to completely remove them from the set of possible pieces. They allow rooks and knights promotion because these pieces are in the set of initial pieces: their rules are already implemented.

csmeyer 2y ago
Oh duh... well my question was not insightful but yes your answer makes sense, there are no bishops on the board lol

billforsternz 2y ago

I don't know why you've put lots of question marks, surely this is completely understandable. The whole point of this was that real chess was too big and complex, hence this dramatically smaller simpler version. There's no bishops in the start position so there's absolutely no way they'd bother implementing the bishop underpromotion corner case. Amusingly enough Rybka, the top engine for many years comparatively recently didn't implement bishop underpromotion either. For a much different reason. The programmer chose a not so great low level bit representation convention that forbid representing this case. He refused to fix the error because it would be too much work for the more-or-less non-existent situations where promoting to a bishop is the best move.

teo_zero 2y ago
Interesting. Does anybody have any example where a promotion to bishop would be preferable to Queen?
- Sesse__ 2y ago
  Basically anything where a bishop would win, but a queen would put the other side in stalemate. For an extreme example, see https://en.wikipedia.org/wiki/Babson_task https://en.wikipedia.org/wiki/Babson_task.
- rdlw 2y ago
  An example from a real GM game: https://youtu.be/CBoS9hSM6oM https://youtu.be/CBoS9hSM6oM
- deleted 2y ago
  [deleted]
- billforsternz 2y ago
  I'm at work so I'm not going to try and do some experiments, but my guess at relative frequency of (under)promotion being the best move (Queen = 1) is something like; Knight 1e-3 Rook 1e-5 Bishop 1e-7 A complicating factor in measuring this is that often a rook serves just as well as a queen, the opponent is going to capture immediately anyway, so players sometimes underpromote to a rook just for the fun factor. My number is more meant to represent cases where underpromotion really is the best move. Knight underpromotion is by far the most important, because a knight can do things a Queen can't, most typically give check to keep a combination going without giving the opponent an opportunity to play an active move. Rook and Bishop underpromotions can only be advantageous when they simultaneously avoid stalemate and keep a winning advantage. This is much more likely with a rook, for example in the famous Saavedra position, perhaps the most famous chess problem of all (it featured as decoration on our wedding cake :).
- seanhunter 2y ago
  It is extremely rare. I saw an example involving Fabiano Caruana(current world #2)[1] and he was visibly excited in the post-match interview and said that's the first time in his whole career (which is thousands and possibly tens of thousands of games especially if you consider online etc) that he had done it. Edit to add: Here's the game. It was Caruana vs Robson 2021 and occurred in the 7th round of the USCF championship. Fabi's final move was to promote to bishop at which point Ray Robson resigned https://lichess.org/study/embed/iLDop9iy/wCdsPJJI https://lichess.org/study/embed/iLDop9iy/wCdsPJJI He did it for style points- a queen would have been just fine in that position. [1] https://youtu.be/Bz-V5wms0pk https://youtu.be/Bz-V5wms0pk

seanhunter 2y ago

Because they modelled the game with no bishops. You don't start with bishops and you also can't promote to a bishop.