The Hardest chess problem in the world? | Hacker News Reader

The Hardest chess problem in the world?

hebdenbridgechessclub.blogspot.com

242 pointsColinWright129 comments

"no longer strictly within the bounds of the rules of the game" I take exception to _strictly_... it's just flat out illegal now, no "strictly" about it. I would have been less ticked off if the article had simply written "no longer within the bounds of the rules of the game."

It is fascinating that the move was formerly legal though.

Yeah, but putting "strictly" there does not change the meaning of the sentence, it's just a superfluous word.

It gives the sentence a nuance that suggests ambiguity, as if prohibition of this move requires some particularly "strict" reading of the rules. I agree that makes the sentence weaker, and given the gravity of the sentence, makes the article seem somewhat amateur.

"strictly" changes the meaning of the sentence. it suggests that there are "strict" and "not so strict" interpretations of the chess rules, and that if you're not so strict, the move is OK.

but promoting to the other color is not allowed, even under "not so strict" interpretations of the rules of chess.

an example of things that may be permitted in "not so strict" chess: taking back your move, not moving a piece even though you touched it, talking to the other player, agreeing to play on even though you've had a threefold repetition.

I mean really, the rules are the rules, and there is no ambiguity. So a "strict reading of the rules" is the same thing as a "reading of the rules." Because, as you say, there is no such thing as a reading of the rules that violates the rules and is thus merely "less strict."

For example, under the rules, not moving a piece you touched and promoting to the other color are the same: illegal.

The examples you are giving are simply cases where the other player is likely to let you break the rules if it's a very casual game.

So again, having "strictly" in the sentence is, technically, purely redundant.

It's a dumb thing to say, but then again, it probably made the piece more suspenseful and thus more fun to read.

You seem to imply that all rules are equally as important as one another, while I would say they are not. For example, in a casual game of chess, most would be okay with some of the aforementioned deviations, like taking back a move. I do not think most would accept it if you started moving your pawns around like queens.

Either English is not your first language, or you have never played a game with a child!

If my opponent would use that move, I would probably consider it as a severe case of rule of cool. ( But this may be the reason, that I prefer RPGs to chess. )

Allowing promotion to any piece sounds perfectly in line with "not so strict" chess rules to me.

I guess the word might've been used in a facetious way, so to speak, the way Mr. Cobb in Inception tells Ariadne (can also be seen in the trailer), "Well, it's not strictly speaking legal" when it's clearly illegal.

But I agree, the word is very misleading in the article's context.

the amount of times i get called bullshit for doing an en passant or uttering the word zugzwang...

Serious question: Does en passant happen often? I've never seen it happen in the wild (i.e. in games I play), but I just play casually with people.

I've definitely seen it, and I have never played a ton of chess.

It happens a lot more to people who don't know the rule.

More common in blitz. Carlsen executes it in the 2013 world blitz championships I believe, and I've had it done to me and I've done it as well in 1m/2s games.

Even if it doesn't actually happen, it often impacts play, especially in the end game.

It's relevant in almost every game, if you include variations that you have to consider when deciding your move.

For an actual legal and cool puzzle: https://www.youtube.com/watch?v=iSKtG-8TwI0

Also cool: white to move and NOT mate

http://www.chess.com/blog/AaronGo/white-to-move-and-not-mate

Would someone like to post a ROT13 of the solution to that, if they have it?

zbir gur gbjre

Qbrfa'g gung serr gur ovfubc gb zngr gur xvat? Gur bayl zbirf V pna frr gung jbhyqa'g qb vg ner gb zbir gur juvgr xvat.

Juvgr xvat pna'g zbir, oybpxrq ol oynpx ebbx naq ovfubc

Vs lbh zbir juvgr ebbx gb p6, gur oynpx xvat vf gura va purpx.

Ubjrire, oynpx pna pncgher gur ovfubc gb ab ybatre or va purpx.

Pna'g lbh zbir gur cnja ng o2 be u2 ol whzcvat bire gur cvrprf va sebag bs gurz fvapr vg'q or gurve svefg zbir? Gur ortvaare ehyrf ba gur fvgr lbh yvaxrq qba'g zragvba jurgure guvf vf n yrtny zbir be abg, fb V'z abg fher.

Except that there aren't any legal moves for the white king, he's caught between the black square bishop and rook on 7th rank.

Ebbx gb P fvk

Zbir gur Ebbx gb n fcbg jurer vg eryrnfrf gur cva ba gur bccbaragf Ebbx, juvpu pna gura pncgher gur ovfubc juvpu unf perngrq gur qvfpbirerq purpx.

Thank you.

Is a castle legal in this case?

No. Castling can only occur if the king has not moved. By convention, white's pieces start at the bottom of the depicted board - the first row. In this puzzle, the king is in the last row, which means it has moved at least 7 steps.

I can't figure it out but I'm positive that 12 year old me would have lost from this position.

Fools mate in an inter-school tournament, the only player on my team to lose his game and thus the only one who didn't get ice cream on the drive home. Still hurts.

EDIT: actually it isn't that hard! I really could cock it up from that position.

Not giving icecream to a 12 year old because he lost a game is just outright cruel. :(

It certainly helps to set a pattern of unhealthy eating.

"You loser! Go eat an apple. Us winners are enjoying this delicious ice-cream".

In Dutch high level youth chess it's usual for there to be a target score for the entire team based on the strength of the opposition that day (say the goal of that day is to score at least 6/10), and then _the entire team_ gets icecream or not depending.

Nah, I was 12. That's old enough to learn about failure in a fairly direct way. It was a good lesson and I'm glad my teacher stuck to it/

Sure, if I'd put up a good fight and lost because he was better, perhaps I'd be a bit sadder, but I really failed. (I still remember it clearly: I was distracted by my opponent's disgusting acne. I also had a turns-out-justified case of impostor syndrome about my place on the team).

That was cool - are there any more of these?

Reminds me of Desktop Dungeons for some reason.

Chess problems are a whole field of puzzles. I don't often see ones that are quite as cool as that but there are absolutely tons of them out there.

SPOILER: Move WhiteRook (G6>C6) thereby giving a check to black King with Knight at (H7). It also blocks WhiteKnight (A8)'s view of the Black King thereby freeing the BlackRook(B7>H7) to kill the WhiteKnight at H7

It's a bishop, not knight.

Sorry mistyped

Forfeit?

I'm a total newbie at chess... but what's the problem with promoting to a queen?

Stalemate.

If white promotes to Queen there are no legal moves for any of blacks' pieces because all the pawns are blocked and the King cannot move into check. It's a stalemate at that point and a draw.

Actually, wouldn't it be that the black King would just capture the Queen?

What moves do you see leading to that?

The king is at C7 and the Queen is at A8 in the video. They king can't do anything. The whole reason to under promote is for white to avoid stalemate when he/she has a winning checkmate.

The only other moves are after white pawn b7 would be to just run the king out of the fork (legal) but then black's whole position collapses and white just cleans up the same as if black plays king B8.

Once the king is tucked in and the D file pawns are blocked he can ONLY move to C7. If he moves out of the fork earlier to C7 or D8 he still loses the rook and the two pawns are still trapped. Against white's D pawn.

edit: We're also talking about this puzzle instead of the original. https://www.youtube.com/watch?v=iSKtG-8TwI0 Which is different and doesn't use old rule loop holes.

As I said elsewhere, you might be responding to a different puzzle (the original) from the one now being discussed (from https://news.ycombinator.com/item?id=10240289 )

Didn't think about that being the reason so many people are talking about capturing the queen.

i don't get it, maybe its because i'm not a huge chess player, but hear me out. The the key to the puzzle was promoting to a bishop, but why not just promote to a queen? A queen can move directions just the same as a bishop. Am I missing something that required a bishop in order to complete this puzzle?

Edit: Thank you for the comment explaining this.

Promoting to a queen would result in a stalemate as the black player would have no legal moves. Promoting to a bishop allows the king to move to the the 8th row, allowing the final checkmate by white

If white promotes to a queen, black will have no legal moves because the king can't move into check, and the pawns can't move at all. If a player can't move, the game is a draw.

When the Queen is placed, it becomes Black's turn. Black is not in check, but is in a situation where there are no legal moves for Black to play (his pawns cannot advance, and the king has no legal squares to land on. Because of this, Black can claim a draw instead of a loss.

I'm sorry for derailing this, but

a) I didn't know that 'Zugzwang' is a word that is used in English, ever

b) That pronounciation reminded me of watching the 'Grimm' TV Series, where everything is German based and the actors talk .. just like that

It's a specific term in chess like castling or checkmate.

I haven't played for ages, but I know the meaning of the word bot in Chess and in general.

It was news to me that this word is used outside of Germany. Looking over localized Chess terms they're either German or French. Interesting export.

I enjoyed the solution...I played chess when I was young but obviously not at an elite level, as I did not know of this rule. But what amused me was -- legal or not -- that I just had never even thought of doing that kind of move, ever. Technicalities aside, it's a nice thinking-outside-of-the-box example.

If chess is a analogy of war and a pawn infiltrates the other side. I believe he has the right to choose a side. I mean he may scale the castle wall only to die releasing a captured prisoner, or he may disrobe a night and get back on the battle field. I love this idea.

I thought defectors were also executed by opposing armies?

Who would want a known traitor in their ranks?

He was a POW.

I would want. Just find a way to use him for your purposes..

Poking around that site's replacement, I bumped into http://www.hebdenbridgechessclub.co.uk/2011/02/11/castling-v.... Also interesting, and involving no-longer-valid rules.

The Anon v Macieja is sweet.

I remember reading about a chess puzzle where a similar "out of the box" thinking was required which would probably put it outside of reach of computer solvers. As a plus it was within currently legal rules.

The winning move was en passant and the solution required observing that the only way the situation could have arisen was the opposite pawn moving 2 ranks forward, making this move possible.

This doesn't seems like the kind of move that would be the crux of a puzzle, tripping up both computer and human. En passant captures are a normal, straightforward move in chess that few above amateur level would overlook. En passant captures are the first move you tend to look at if an opponent has moved their pawn two spaces adjacent to one of your own.

> En passant captures are the first move you tend to look at if an opponent has moved their pawn two spaces..

GP is clearly saying that you're not given the information that a pawn has moved two spaces, the trick of the puzzle is to infer from the board's layout that such must be the case.

Seems damned clever to me. From a quick google it appears that such things are known as "retrograde puzzles".

Also very challenging for chess players is retrograde analysis, where you have to find the only possible legal moves to reach the given position.

See the cover of this book by Smullyan http://ecx.images-amazon.com/images/I/81y-bMMYCoL.jpg

Thanks for that link, it was fun and took me quite awhile to figure out!

Vs gur obneq vf hcfvqr-qbja, juvgr cebzbgrq gb n ovfubc naq gura oynpx zbirq bhg bs purpx. Bgurejvfr V pna'g guvax bs nalguvat. Vf gung jung lbh pnzr hc jvgu?

V guvax juvgr unq n xavtug ba o6, zbirq vg gb n8 naq gura gur oynpx xvat pncgherq vg.

> "I first encountered this position in June 1937 [...]"

OT remark: Jesus. I work with the elderly, mostly. I would love to have her clarity of thought if and when I reach her age. I've heard before that playing chess retains hair loss and mental deterioration, especially in the elderly.

I, too, was curious about Lady Cynthia Blunderboro. It seems she's a fictional persona prone to hoaxes.

https://www.google.com/search?q=lady+cynthia+blunderboro

The fact that she by chance happened to have the very same position during normal play gave it away. The probability would be astronomically low.

The coincidence isn't quite what you think it is.

In the story world, the puzzle probably took its precise form from that game. If the game hadn't happened, maybe Anderssen's unpublished notes would have included a similar puzzle, or maybe nothing along those lines. So the coincidence is "merely" that she's related to the person who played the game that begot the puzzle.

Not sure if you're referring to something else. But in the story she is just replaying the game that her grandfather played back in the 1800s. She didn't actually come up with that move from playing.

You ruined everything :-P

> retains hair loss

I don't think I understand.

s/retains/inhibits.

If we are playing fast with the rules re sides, was there any rule at the time saying the black King couldn't take the black Knight?

That would break the check, force white to move the rook to block, allow the black king to take the rook, and place black in a winning position.

> "force white to move the rook to block"

A better move would be to just move your king out of check and to go protect your rook.

From FIDE rules:

> When a player, having the move, plays a pawn to the rank furthest from its starting position, he must exchange that pawn as part of the same move for a new queen, rook, bishop or knight of the same colour on the intended square of arrival.

> promotion: 3.7e. Where a pawn reaches the eighth rank and is replaced by a new queen, rook, bishop or knight of the same colour.

https://www.fide.com/fide/handbook.html?id=171&view=article

Thank you for the reference - appreciate that.

I wonder when that explicit rule was introduced. It says in the article:

  "But in fact, at the time this game was played
   there was no specific rule stating that a pawn
   had to be promoted to a piece of the same colour!

Sarratt in his Treatise on the Game of Chess (1808) says:

"When a player has pushed a Pawn to Queen, he is at liberty to make a second Queen, a third Rook, or any other piece which he may deem more useful for his attack or defense".

While this doesn't explicitly say that he must promote to a piece of the same color, it implies it. After all if the piece could be promoted to either color it would make sense to say a third queen or a fifth rook rather than a second or third.

That doesn't really imply much. Having a fifth rook does not correlate at all to having a piece of the same or opposite colour. Regardless, based off that rule, a piece of the opposing colour would be defined by "any other peice [sic] which he may deem more useful for his attack" in that play, so it sounds perfectly legal to me.

If you arrange your game just right, you can legally have up to ten rooks (or bishops or knights, or nine queens) of the same color on the board at once. (This will probably not be possible without the cooperation of the other player.)

Not at all, it would be a third Rook of the alternate color.

I wonder why it was introduced.

The article states clearly, more than once, that the move is not legal by current FIDE rules.

More on the rule history and this puzzle.

https://en.wikipedia.org/wiki/Promotion_%28chess%29#1862_Bri...

"The broad language of Law XIII also appears to allow promotion to any piece of either color. This led to the whimsical endgame study diagrammed at right. White is to play and checkmate in one move."

reminds me of "0-0-0-0". Before the rule was added that castling was a 'row move', you could promote an e-pawn to a rook and than castle superlong by moving the king from e1 to e3 (and the rook to e2). This oversight in the rules was later corrected.

I'm not much of chess person, but I don't get it. Even if the black knight plays for white, it's still not checkmate. What prevents the black king from "eating" that black knight?

The black knight plays for black.

In the solution presented at the end of the article, whose turn to move is it? Who can't make any further moves coz they've been check-mated? That's what I don't get. If it's white, white can still move their king back towards their home row and there's more than one move left in the game. If it's black, black can move the black knight in between the two kings and we'd still have more than one move left.

Black is in check from the white rook. Moving the black night doesn't escape the check, so isn't a legal move.

Now I get it. The "beef" is that white replaced their white pawn with their opponents black knight, which of course the black king can't eat...

White advanced the pawn and promoted it. It is black's turn. Moving the knight between the kings is illegal because the black king is in check by the white rook.

Black plays for black. The black knight blocks the only position that the black king can move to for safety, all other moves by the black king (or not moving the king at all) result in the king being captured. If it moves right it gets captured by the rook, move down or down-right, it gets captured by the white king. Don't move and it gets captured by the rook, and there's no way to play the black knight to block the rook, either.

Of course you could argue that if you're ignoring today's rules of the game that you may as well have the black king take the black knight, but that's illegal under the rules and probably has been right from the start.

The problem isn't showing up for me, but cached version:

http://web.archive.org/web/20150918165831/http://3.bp.blogsp...

White to play and mate in one.

Why is it illegal now? I think it would be more fun if is was legal for the very, very, few cases where it can actually help a player.

A poorly phrased question that lacks context != cleverness

The "puzzle" relies on an obscure situation which isn't even a rule. You might as well claim that the kings can checkmate each other, or that the rook can spontaneously transform into a queen.

HEY GUYS CHECK OUT THIS FAKE PUZZLE THAT REQUIRES YOU TO IGNORE EVERYTHING YOU KNOW ABOUT CHESS RULES FOR IT TO WORK

Huh? The solution doesn't require you to "IGNORE EVERYTHING YOU KNOW ABOUT CHESS RULES". I can't speak for all casual players but this is a rule that seems technically possible but just never executed because it's hard to conceive a situation in which it would ever be used in practice. For those of us who don't know this specific rule, there's no excuse for us not thinking-outside-of-the-box...and learning of the "solution" is enjoyable.

Life is full of rules in which the exception was never addressed or outlawed because the exception was never even considered. [Insert Kobayashi Maru trope here]

Not really, it's an illegal move which makes it a puzzle from a different game of chess.

Clickbaity title.

It's not a rule now. This move was legal at the time.

You can reasonably object that you shouldn't be expected to know that history, but that makes it quite different from "rook can spontaneously transform into a queen" and similar.

I think you're just disappointed because you wanted to solve a chess problem. I liked the article because I read it as a story to be enjoyed rather than a problem to be solved.

Yeah I would be disappointed too if, for example, I'm asked to find out how to avoid a clear checkmate and I spend a lot of time thinking and fail, and then I'm told "you flip the board over and run away".

It doesn't take long to go through all of the permutations in your head and figure out that it's something really odd, but this line in the second paragraph should have let every reader know that the solution was gimmicky: "If I told you that the solution is a VERY unusual move that is no longer strictly within the bounds of the rules of the game then that might help you a little bit." From then on, I read the story instead of trying to solve the problem.

He said at the very beginning of the article that it is no longer a legal move. I don't know why you are surprised to find out that the move isn't legal now. But it has nothing to do with "flipping over the board". It's a perfectly reasonable seeming move.

Marketing problem-solving and delivering history is linkbait, and I dislike bait-and-switch equally among journalism and retail. It's deceptive and the article doesn't deserve the clicks it's getting.

Name it "An interesting historical chess rule" and let the chips fall where they may. (I wouldn't have clicked that FWIW)

I didn't click it myself until it got a lot of votes, and now I'm glad I did. It's not hard to figure out why it would be relevant to the audience here. Applying the lesson in a different context might be difficult though.

SPOILER ALERT

I don't know about "hardest" but I do tend to wonder: who'd have thought to promote to anything other than one's own color? Kinda feels similar to doing some odd operation "in a single processor instruction" but the trick is that the ISA in question went the way of the dodo about four decades ago.

I moved the pawn down one space, assuming the board was backwards and the white pawn was on the second rank.

That's not mate, the black king can move diagonally to G1. Same thing black would do if white promoted to a white piece.

This is interesting, but as the author acknowledges, not legal in modern games.

Another famous position which relies on (legal) underpromotion: https://en.wikipedia.org/wiki/Saavedra_position

The article is interesting, but the title is frustrating because clickbaiting. I personally love chess and love challenges, and this was downright disappointing. I don't encourage clickbaiting. This is a shame because the article is interesting

Harder problem is to find a sequence of turns, where white always wins, from starting position.

Anyway this turn is not legal in chess I learned.

Definitely an interesting hack, it's interesting that the rules were updated to make it illegal.

For a really good problem, with legal moves, feast on this:

http://gameknot.com/analyze-board.pl?bd=0&fen=8/3P3k/n2K3p/2...

That's the best example of out-of-the-box thinking I've ever seen in chess.

Can't the knight capture the white king resulting in checkmate for black?

No, it'd have to be in the position of the white pawn in the initial position to reach the king. It moves two pieces (not three) horizontally and 1 piece vertically, or vice versa.

Could it also have been a black rook as well?

No. A Black rook would have allowed black to b8b7 and block the white rook from the final checkmate. A knight, on the other hand, would not be able to block the white rook and would therefore result in a checkmate.

not really valid as white becomes black.

Did you actually read right to the end?

  "But in fact, at the time this game was played
   there was no specific rule stating that a pawn
   had to be promoted to a piece of the same colour!

Of course there was also no rule saying that chess functioned on a restrictive rules system and a lot of evidence that it instead functioned on a permissive system. Which would invalidate the "no rule says I can't" argument.

(when designing a game's rules, "restrictive" means the approach is "everything is permitted by default, unless explicitly restricted", while "permissive" means "everything is forbidden by default unless explicitly permitted" -- if we assume that chess is a restrictive-rules game, we can similarly mate in one from almost any position by simply inventing new pieces with unusual abilities and declaring that "the rules don't say you can't!")

If the rule was simply, "A promoted pawn may be exchanged for any piece," then that would fit within a permissive system, and still qualify as "nothing says you have to promote to the same color."

So, promoting a pawn in chess is undefined behavior?

No, its defined (both then and now), its just the spec has had breaking changes from earlier versions.

No. It was unclear whether you could promote to a piece of the other colour, but a conforming implementation of chess will not make demons fly out of your nose.

Can it be called promotion then, it is like country A promoting its soldier to general of country B.

What will happen it is not endgame. Who will move the black knight promoted by white side?

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