Illegal Position Contest!

White has doubled pawns but black isn’t missing any pieces.

Sightly harder one.

Doubled pawns so white had to take one of nlacks pieces, his dark squared bishop. Black also had to take whites dark squared bishop, but white dark squared bishop wouldn't be able to get if blacks bishop which had to be taken on a dark square was taken on c3. Therefore c4 and bxc3 is the only alternative but that means whites bishop couldn't have gotten out with the b2 and d2 pawns.

This one is much harder to prove illegal because it's legal.

Missed the fact the b-pawn could move, good job!

Here's another proof game for #8269. It's better because it's shorter and because it ends with a move by White.

just trying to figure out... 3?

super illegal position #2

I can see the advantage of it being shorter (didn't notice till I got to the end that a black knight had disappeared as well as Black's dark squared bishop). But what's the advantage of finishing with Black on the move when @SeaWing7000's FEN says it's White?

Actually I should have posted this

because my first attempt failed to match @SeaWing7000's ply count under the 50 move rule.

In a composition, the only part of the FEN that matters is the piece placement data. Anything else (side to move, castling rights, en passant target square, move count) is ignored.

Ending with a move by White is a matter of simple common courtesy.

"What?" you say. "What kind of sense does that make?" The idea of applying common courtesy to a proof game is a new concept recently developed by EndgameEnthusiast, who unfortunately got it backward and thought all proof games should end with a move by Black.

I could make a proof game in 13.0, but that wouldn't end with a move by White.

Then the title of the thread needs to be

Illegal Diagram Contest!

Where does one find the rules you mention?

The definition of "position" is unclear or perhaps I should say "ambiguous". Sometimes it refers to the "full information" state of a game, sometimes only to the piece formation on the board as displayed in a diagram. All rules about the latter come from the composition world since game positions are always full game states! If I remember well, FIDE fails to do its part in the laws as it should emphasize that all FIDE laws operate on known states - unless the laws say otherwise when handling accidents! --- for instance you cannot claim a move is illegal or legal or playable or unplayable because of an unknown property in the full game state.

That is the reason why game players must keep record of underway games. Arbiters demand full information.

The rules for compositions are at https://www.wfcc.ch/rules/codex/

Article 14 of the Codex talks about illegality of positions. I don't think the thread title can be changed and wouldn't be a good idea anyway since it would confuse people and we have enough confusion here already.

In case someone may be curious, here's one of many proof games in 13.0.

I did believe you - even checked (and matched the ply count).

But I still think the rule that all positions should be taken as Black to play is ridiculous and nowhere to be found. I remember having an argument with a Wikipedia editor who insisted that all problems should be White to play, which is at least more natural.

By the way WFCC excludes illegal positions as compositions, I think.

A proof game has something in common with a helpmate where the convention is a final move by White, but then the convention is also an initial move by Black which wouldn't normally occur from the starting posiagram in any proof game.

Buh

Don't say nowhere. The rule for Black to play is found in my tongue-in-cheek remark above, and the similar rule for White to play is found in many comments here by EndgameEnthusiast.

The Codex says illegal positions are not acceptable for composition tournaments unless the tournament conditions so stipulate. This thread is not a composition tournament, and illegal positions are not just acceptable but required.