busterlark wrote:
Maybe? But it seems a little clumsy, throwing in three pawns just to make this position...
Illegal Position Contest!
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I guess I could try throwing in a fourth pawn at b4, but then it's like... four pawns just to get this position. There should be something a little simpler...
EDIT: Idk, here's the best I can come up with for that idea. But this idea is just starting to feel a little clumsy, I think. Too many pawns:
busterlark wrote:
I guess I could try throwing in a fourth pawn at b4, but then it's like... four pawns just to get this position. There should be something a little simpler...
A fourth pawn at b4 wouldn't make the position illegal.
The good illegal positions in this thread are the ones whose illegality is challenging to prove. They don't need to be simple.
What was an example of one that was difficult to prove, if you don’t mind my asking?
busterlark wrote:
What was an example of one that was difficult to prove, if you don’t mind my asking?
I don't mind. See if you can correctly explain why this position is illegal.
I would only be able to guess, I wouldn’t be confident in any sort of explanation. I would guess it’s your reason 6, though, one side reached their position but the other side didn’t have enough tempi to reach their position. But again, just a guess.
If you are only able to guess, I suppose it means you agree this one is challenging to prove illegal. But if you are right that there is a tempo shortage, you could start by trying to prove that the position would be legal if the black pawn at a4 were at a3.
I do agree that it’s challenging. I think that I haven’t spent enough time thinking about illegal positions to properly appreciate this, but I do appreciate the example and the explanation. Always interesting to learn what people who understand things at a higher level think. Thank you!
busterlark wrote:
I do agree that it’s challenging.
But your guess about the reason was correct, and White is one tempo short. Proving it in this case requires constructing a proof game with the extra tempo provided by having the a4 pawn end at a3. Here is one such proof game.
It feels sort of like a mathematical proof, doesn’t it? Proof by contradiction, kind of.
Kind of. Any illegality proof could be framed as a proof by contradiction. We often start by assuming a position is legal and drawing conclusions based on that assumption. At some point we will reach a contradiction if the position is illegal (and if our reasoning is sound).
Here's another easy position, intended as a warmup for those who have recently started reading this thread. What makes this position illegal?
Nov 15, 2021
0
#5895
n9531l1 wrote:
Here's another easy position, intended as a warmup for those who have recently started reading this thread. What makes this position illegal?
The c-pawn :/
n9531l1 wrote:
Here's another easy position, intended as a warmup for those who have recently started reading this thread. What makes this position illegal?
I see why it's illegal, but I think you meant for other people to figure it out, so ill wait
Nov 15, 2021
0
#5897
meowmeomeo wrote:
n9531l1 wrote:
Here's another easy position, intended as a warmup for those who have recently started reading this thread. What makes this position illegal?
The c-pawn :/
Why is that?
meowmeomeo wrote:
The c-pawn :/
There are two c-pawns on the board, neither with a very direct connection to the illegality. I suspect this "proof" was meant as a joke or an attempt to make fun of the position for being too easy. But to be more generous, maybe it was meant as a helpful hint to the inexperienced solvers.
Should I give the answer I found?
That one might be a little too easy. Black has no legal retraction to uncheck the white king.
Illegality reason #4 at https://www.chess.com/forum/view/fun-with-chess/illegal-position-contest?page=297#comment-64963705
I mean, to some extent, they're all going to be reducible to your reasons, aren't they? Hard to imagine a position that will bypass all of your reasons.
It's easier for me to imagine "reason 4" positions. Here's another I'm trying to noodle through. Maybe? But it seems a little clumsy, throwing in three pawns just to make this position...