Is this position legal? - Chess Forums - Page 68

chaotic_iak

Jan 19, 2016

0

#1341

lal_badam wrote:

how to decide a position is legal or not ?

silvia_trench wrote:

how can chess.com members decide it is legal or not ?

Is there a standerd methode ?

Welcome to the world of retro puzzles. Just use logic to decide it. For example, you can tell that these are all illegal easily:

Meanwhile, these ones are legal, although not as easily:

The good ones in this thread are just these made more complex.

No, there is no method to always determine them easily.

BigDoggProblem

Jan 19, 2016

0

#1342

silvia_trench wrote:

chaotic_iak wrote:

lal_badam wrote:

how to decide a position is legal or not ?

silvia_trench wrote:

how can chess.com members decide it is legal or not ?

Is there a standerd methode ?

Welcome to the world of retro puzzles. Just use logic to decide it. For example, you can tell that these are all illegal easily:

Meanwhile, these ones are legal, although not as easily:

The good ones in this thread are just these made more complex.

No, there is no method to always determine them easily.

the last one is illegal as no one can give double check like this

Not so! There is a way.

wilford-n

Jan 19, 2016

0

#1343

silvia_trench wrote:

chaotic_iak wrote:

Meanwhile, these ones are legal, although not as easily:

the last one is illegal as no one can give double check like this

Yes, it is legal, just tricky. Here's the position before White's last move:

Don't forget about en passant.

Now the one above it, I just can't see. Black's rook could not have been anywhere else on his last move, and his king could not have been on g1 either. It looks illegal to me. Solution anyone?

BigDoggProblem

Jan 19, 2016

0

#1344

wilford-n wrote:

silvia_trench wrote:

chaotic_iak wrote:

Meanwhile, these ones are legal, although not as easily:

the last one is illegal as no one can give double check like this

Yes, it is legal, just tricky. Here's the position before White's last move:

Don't forget about en passant.

Now the one above it, I just can't see. Black's rook could not have been anywhere else on his last move, and his king could not have been on g1 either. It looks illegal to me. Solution anyone?

Last move = ...exf1=R+

wilford-n

Jan 19, 2016

0

#1345

BigDoggProblem wrote:

Don't forget about en passant.

Now the one above it, I just can't see. Black's rook could not have been anywhere else on his last move, and his king could not have been on g1 either. It looks illegal to me. Solution anyone?

Last move = ...exf1=R+

Nice. I didn't think about underpromotion...

wilford-n

Jan 20, 2016

0

#1346

mshinde wrote:

every position is legal position if u consider chess 960

No. Just no. See the first two positions in post 1429. Neither is legal, 960 or otherwise.

ThrillerFan

Jan 20, 2016

0

#1347

mshinde wrote:

every position is legal position if u consider chess 960

Not true, here's an illegal position, even in chess 960, because in chess960, the King must start between the two rooks, and clearly the two knights started on a1 and b1:

Robert_New_Alekhine

Jan 20, 2016

0

#1348

ThrillerFan wrote:

mshinde wrote:

every position is legal position if u consider chess 960

Not true, here's an illegal position, even in chess 960, because in chess960, the King must start between the two rooks, and clearly the two knights started on a1 and b1:

Or else the rooks were captured on their home squares...

chaotic_iak

Jan 20, 2016

0

#1349

It has been a long time since I constructed chess problems, oh well. Not very interesting nor aesthetically pleasing, but eh.

EDIT: Oh, and my intended solution has a shortcut, even. Oh well; I did say it's not very interesting.

(11+13) Is the position legal?

delta5ply10

Jan 20, 2016

0

#1350

no

The_Ghostess_Lola

Jan 20, 2016

0

#1351

Is this position lethal ?

wilford-n

Jan 20, 2016

0

#1352

chaotic_iak wrote:

It has been a long time since I constructed chess problems, oh well. Not very interesting nor aesthetically pleasing, but eh.

EDIT: Oh, and my intended solution has a shortcut, even. Oh well; I did say it's not very interesting.

(11+13) Is the position legal?

Yes. Black's king's rook was captured, so it doesn't matter that it has no path to emerge from behind the pawns. The other rook came from underpromotion of the a-pawn on f1, which is possible if all missing white pieces (both knights, a rook, a queen, and the f-pawn) were captured by it.

White's rook must have emerged from behind the pawns via the f-file after his f-pawn made a capture on e3 (which was subsequently captured by Black's pawn on its way to promotion).

The last move played was Black's Ne1-c2.

EDIT: Changing my answer to no, because White's light-square bishop has no path from behind the pawns, and it can't be the result of underpromotion due to the requirement that Black had to capture the missing pawn in order to reach f1.

DavidMertz1

Jan 20, 2016

0

#1353

The_Ghostess_Lola wrote:

Is this position lethal ?

It's legal, anyway.

wilford-n

Jan 20, 2016

0

#1354

DavidMertz1 wrote:

The_Ghostess_Lola wrote:

Is this position lethal ?

It's legal, anyway.

And lethal.

Death by enforced gluttony!

Remellion

Jan 20, 2016

0

#1355

wilford-n a écrit :

Yes. Black's king's rook was captured, so it doesn't matter that it has no path to emerge from behind the pawns. The other rook came from underpromotion of the a-pawn on f1, which is possible if all missing white pieces (both knights, a rook, a queen, and the f-pawn) were captured by it.

White's rook must have emerged from behind the pawns via the f-file after his f-pawn made a capture on e3 (which was subsequently captured by Black's pawn on its way to promotion).

The last move played was Black's Ne1-c2.

EDIT: Changing my answer to no, because White's light-square bishop has no path from behind the pawns, and it can't be the result of underpromotion due to the requirement that Black had to capture the missing pawn in order to reach f1.

It is legal, though. Hint: are you sure black promoted on f1, and not on some other square?

SMSAmanda

Jan 20, 2016

0

#1356

Definitely 2 and 3

2.

3.

The_Ghostess_Lola

Jan 20, 2016

0

#1357

DavidMertz1 you're wonderful for taking out the time to put that 2gether........

....and wilford-n you are awesome for the checkmating solution !

TY you two....xoxo....Lola

wilford-n

Jan 20, 2016

0

#1358

Remellion wrote:

wilford-n a écrit :

Yes. Black's king's rook was captured, so it doesn't matter that it has no path to emerge from behind the pawns. The other rook came from underpromotion of the a-pawn on f1, which is possible if all missing white pieces (both knights, a rook, a queen, and the f-pawn) were captured by it.

White's rook must have emerged from behind the pawns via the f-file after his f-pawn made a capture on e3 (which was subsequently captured by Black's pawn on its way to promotion).

The last move played was Black's Ne1-c2.

EDIT: Changing my answer to no, because White's light-square bishop has no path from behind the pawns, and it can't be the result of underpromotion due to the requirement that Black had to capture the missing pawn in order to reach f1.

It is legal, though. Hint: are you sure black promoted on f1, and not on some other square?

Yes, I'm pretty sure. He couldn't have underpromoted on a1, the only other promotion square the pawn could reach, because the new Black rook has no way to get over to f1 from there. White's c1 bishop hasn't moved, so he couldn't get out from behind the pawns via the c-file without eating it first, nor could he have traversed the rank. So I'm sticking with no, but if you see another way, enlighten me. Inquiring minds want to know.

Remellion

Jan 20, 2016

0

#1359

wilford-n a écrit :

Yes, I'm pretty sure. He couldn't have underpromoted on a1, the only other promotion square the pawn could reach, because the new Black rook has no way to get over to f1 from there. White's c1 bishop hasn't moved, so he couldn't get out from behind the pawns via the c-file without eating it first, nor could he have traversed the rank. So I'm sticking with no, but if you see another way, enlighten me. Inquiring minds want to know.

Black's pawn went axbxcxd, promoted to a rook on d1, capturing 2N and Q. White's f-pawn went fxgxh7xg8=B, capturing N, Q and R (the black rook was captured on h7 or g8. The last move was ...Ne1-c2+, no capture. White's f1-bishop and a1-rook were captured by pieces not pawns. Black's king entered behind the pawns from b3-c2.

The_Ghostess_Lola

Jan 20, 2016

0

#1360

....didya haftoo IM pfren ?