Illegal Position Contest!

It's illegal because of the pawns, not the kings position.

What is it about the pawns that makes the position illegal?

He means that the pawn structure PLUS the capture on f4 is illegal. Nevertheless the position is legal with just the 14 white captures. In several ways.

Note that black's [Ph7] promoted on e.g. g1 after a capture before it was captured itself. And that white cannot have captured e.p. on e6 as this loses [Bf8].

I'm confused about whether you're saying the position at #7783 is legal or illegal.

I concluded that it's illegal, but would be legal if the e6 pawn were on f5, and was going to suggest that Leither post it that way in the Shortest Proof Game thread.

I first tried to explain how EndgameEnthusiast2357 thought it was illegal. Next I stated it was legal - in several ways - without explaining it. To leave everyone a bite at the cherry. Somebody will find one of those ways, not?

Btw, Leither wanted you to fall for the e.p. trap. But then you would first have to see the option of course!

The four ab pawns on the 4th and 6th ranks came from the cdef files and the e6 pawn came from g2 after two captures, regardless of whether one of them was an e.p. so I'm not sure what the e.p. trap is.

I can make a proof game with the e6 pawn still at f5, but I haven't found any of your several ways to reach the posted position. Before I look any further, I'd like Leither to confirm your suggestion that a legal position was deliberately posted to fool people into coming up with bogus illegality proofs.

I have now seen that my position is indeed legal. Black was supposed to be unable to promote all the pawns, but I had completely forgotten that two of them do not have to promote.

Alright then. I can swap the bishop for a knight to create a completely new illegal position. In fact, it is substantially different from my first one.

In your position at #7783, what were the first retractions for each side?

I thought I had figured it out, but realized I was still a move short. So I'm still working on making #7783 legal.

Don't see any substantial difference. Neither the knight nor the erstwhile bishop could have discovered check fron the c1 bishop. Or am I missing something?

It took me too long, but here is one way for #7783.

I suggested the opposite. He posted a diagram he thought was illegal but he hoped solvers would believe legal with the help of an en passant move. Composers always try to lure you into believing something that is untrue! His effort failed because (a) no solver detected the e.p. possibility in the first place (b) his assumption that the digram was illegal was wrong!

#7955 is perfectly illegal!

Yes, I misunderstood your suggestion. Now I'm hoping you'll challenge us to figure out why the new position is also legal. So far it looks illegal to me.

Edit - Just saw your previous comment, probably about #7795.

Yes, I was missing something (everything).

And the substantial difference beween #7783 an #7795 is that one is legal and the other isn't.

?

We aren't to #7955 yet, my post is #7805.

Oops! In that case we have to assume that #7955 is legal until it appears! Innocent until proven guilty

I predict #7955 will be a re-post by KieferSmith of the legal position at #7799.