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No reachable chess position with more than 218 moves

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Re: No reachable chess position with more than 218 moves

#81

Post by jibal »

kevindamm wrote: post #77
jibal wrote: post #66

Earlier quoted context omitted.

The 3 repetition draw rule has no bearing on the number of possible chess positions. And for the number of possible moves in a game the 50 moves with no capture or pawn move rule is a much more stringent limit. BTW, the 3 repetition rule only comes into play is one of the players invokes it ... games can legally have more than 3 repetitions, but not more than 5 repetitions.

I didn't know it required a player to invoke it, I was basing the statement on chess implementations I've read (and written) where it kicks in automatically... but the 5-time limit you mention still supports my case that there's an upper limit. As long as the number of pieces remains the same, there are a finite number of arrangements for them so eventually (after a finite number of moves) a position would be repeate…

Your "case" that there's a limit isn't in question ... as I said, the 50 move rule is a far more stringent limitation. And those 50 moves cannot include repetitions--they are captures and pawn moves, which are irreversible.

If you read my comment that you responded to carefully, you will find that it is precise and accurate--as I said, the repetition rule has no bearing on the number of positions.

This horse is dead, so I'm moving on.

Re: No reachable chess position with more than 218 moves

#82

Post by systoll »

contravariant wrote: post #49
pmontra wrote: post #48

Earlier quoted context omitted.

The caption of the last diagram is "Legal but non-reachable position with 271 moves for White. Corner queens can be replaced with bishops." There are 24 white queens.

That's the difference between illegal an unreachable. To reach that position you'd need to start from a different point (start both sides with 16 pawns or w/e), but you wouldn't need to break any other chess rules.

If you can start from any arbitrary different point, you can just start from the point you’re intending to reach, and don't need to break any other rules.

As per FIDE rule 3.10.3 "A position is illegal when it cannot have been reached by any series of legal moves". The position isn't legal per FIDE rules.

Beyond there being too many queens… black could not possibly have made the last move. For white to have any moves right now, the last move must have been black moving the king to H8. But G8, G7, H7 are all occupied, so where could the King have moved from?

Re: No reachable chess position with more than 218 moves

#83

Post by InitialLastName »

sim7c00 wrote: post #72
dmurray wrote: post #64

Earlier quoted context omitted.

I believe 8848.5 under modern rules (with the 75-move rule, as in FIDE rules since 2014). There's a reasonably rigorous demonstration here: https://wismuth.com/chess/longest-game.html

how can the longest game have half a move???

"Moves" are counted for both players. Half a move means White moved but Black hasn't yet.

Re: No reachable chess position with more than 218 moves

#84

Post by kelipso »

stavros wrote: post #59
codeulike wrote: post #10

They dont really spell it out but they mean "from this position the player has 218 possible legal moves to choose from"

Ah, wow, I read the article wrong all this time, thank you. I thought they meant "the maximum number of moves you can make to reach any chess position is 218", and I was wondering why the article made no sense to me.

Is that weird? I feel like it’s plausible though. Very rare to have chess games with more than 200 moves.

Re: No reachable chess position with more than 218 moves

#85

Post by [deleted] »

jibal wrote: post #81
kevindamm wrote: post #77

Earlier quoted context omitted.

I didn't know it required a player to invoke it, I was basing the statement on chess implementations I've read (and written) where it kicks in automatically... but the 5-time limit you mention still supports my case that there's an upper limit. As long as the number of pieces remains the same, there are a finite number of arrangements for them so eventually (after a finite number of moves) a position would be repeate…

Your "case" that there's a limit isn't in question ... as I said, the 50 move rule is a far more stringent limitation. And those 50 moves cannot include repetitions--they are captures and pawn moves, which are irreversible. If you read my comment that you responded to carefully, you will find that it is precise and accurate--as I said, the repetition rule has no bearing on the number of positions . This horse is dead…

[deleted]

Re: No reachable chess position with more than 218 moves

#86

Post by jobigoud »

The black pawn on b2 is eating a lot of possible moves for the other pieces…

It has only one legal move, take the Knight on c1. If that pawn wasn't there it would free that square for 4 white queens and a Knight. But of course the black king would already be in checkmate so these moves wouldn't really be available.

Tempting to put that e5 Queen elsewhere so that it doesn't immediately checkmate and leave the b2 square available for others.

edit: I imagine that pawn also needs to survive that far in order to avoid a stalemate.

Re: No reachable chess position with more than 218 moves

#87

Post by stavros »

kelipso wrote: post #84
stavros wrote: post #59

Earlier quoted context omitted.

Ah, wow, I read the article wrong all this time, thank you. I thought they meant "the maximum number of moves you can make to reach any chess position is 218", and I was wondering why the article made no sense to me.

Is that weird? I feel like it’s plausible though. Very rare to have chess games with more than 200 moves.

Yeah I kind of thought that it meant "you can get to any valid position in 218 moves max", it was hard to parse.

Re: No reachable chess position with more than 218 moves

#88

Post by tromp »

jobigoud wrote: post #86

The black pawn on b2 is eating a lot of possible moves for the other pieces… It has only one legal move, take the Knight on c1. If that pawn wasn't there it would free that square for 4 white queens and a Knight. But of course the black king would already be in checkmate so these moves wouldn't really be available. Tempting to put that e5 Queen elsewhere so that it doesn't immediately checkmate and leave the b2 squar…

The black b2 pawn has no moves in the position with white to move. If it were black's move, it would still have no moves since it is pinned by the white queen on e5. If it were not pinned it would have 4 moves, as it can also underpromote.

Re: No reachable chess position with more than 218 moves

#89

Post by NickC25 »

Just want to give Lichess a shoutout here. They are fantastic, provide great content, have things for free that you need to pay for on Chess.com, and a fantastic amount of variants.

Even better, the level of play in those variants, like 960 or Crazyhouse, is MUCH higher on Lichess than on Chess.com.

Re: No reachable chess position with more than 218 moves

#90

Post by [deleted] »

kelipso wrote: post #84
stavros wrote: post #59

Earlier quoted context omitted.

Ah, wow, I read the article wrong all this time, thank you. I thought they meant "the maximum number of moves you can make to reach any chess position is 218", and I was wondering why the article made no sense to me.

Is that weird? I feel like it’s plausible though. Very rare to have chess games with more than 200 moves.

[deleted]
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