Magnus Carlsen new chess variation: he trolled his team in this video

Weird changes in the rules usually give white a forced win somewhere or another :) Black learned yet again that copying white never works :) But yeah... ...c6 early on should avoid disaster, though white clearly is getting ahead in development. Magnus did say he tricked him.

So this is what I understand it to be:

"Piece to c7 CHECKS the king - which can't move to d8 because the piece is now a bishop - but next move the c7 piece could CAPTURE on e8... what a mate!"

Actually wait a minute... is Bxc7 actually check/checkmate? Checkmate means that you make it so that your opponent can't prevent the king's capture next move, right? But couldn't black just play any old move, say, ...h6, and avoid his king getting captured? Next move Magnus would not be able to take black's king on e8 because his piece on c7 will be a bishop. So it's hard to see how black was in check in the first place. The knight on c7 was never threatening the king on e8 because it wouldn't be able to execute the threat next move. 

When you said "next move," solskytz, you reminded me of the true definition of checkmate :) It's always about what you're threatening to do next move, and here the "knight" on c7 wasn't threatening to do anything.

Normally when you can draw an l shape from a knight to a king, it means check, but because of the piece changing rule, you can't conclude that anymore.

Confusion and more confusion. 

Staying on this thread and going deeper into this causes an IQ decrease in the long term - 20 points per page, I suspect.

Finally (at page six perhaps?) the brain turns into light-green jelly and slowly exits the skull through the ears and nostrils. 

Marco is staying remarkable silent... and is laughing all the way to the bank. 

Not all details are given at the beginning, some are shown during the game, and they stay consistent until the end when Carlsen claims mate.

It all makes sense though as far as I can tell (but I've been wrong a bunch of times already so you never know). I thought it was pretty interesting. Check isn't purely defined by whether a piece lines up with the king, it's just that it always seemed that way because our pieces always threaten the same thing each turn. But when you change that, now you can't use that as a way of identifying check, anymore. Check is still clearly defined, we just need to be more diligent in how we apply the rule now to avoid getting confused :)

I think that's pretty cool. But it looks like Magnus was wrong, then. His Bxc7 wasn't check or checkmate.

Anyone have the chess rules handy on them? :) I'm pretty sure check and checkmate is always defined by what you can do on the next move. So if white's knight will become a bishop next move, black's king on e8 has nothing to worry about and doesn't even have to move.

By the way, looking at the pictures now, it seems 3...Kxd8 was good, because white's queen is trapped.

When it lands on d8 it would be a bishop... but it can land on d8 so...

(look at my pictures, all minors don't change every ply, your pieces only change after your move.)

I dunno, this is what wikipedia says anyway :p

"A response to a check is a legal move if it results in a position where the king is no longer under direct attack (that is, not in check)"

So black could respond to Bxc7 with ...h6, and on Magnus's turn, black will not be in check, so black did legally get out of check if he even was in check.

Like I said to you on the first page, if all minors change every ply, then white's 2nd move is illegal.

Right, but in a later post I said that only your pieces change every ply, not your opponent's. In other words white's half-moves change white's pieces and black's half-moves change black's pieces. This must have been what Magnus meant because he plays consistently with that.

If you mean "your pieces change after you move" then yes, he is consistent with that.

And in that case after 4...h6 the move 5.Nxd8=B is legal. So it's not safe for black to play 4...h6

If you mean one player's minors change every ply (white's) while black's change every other ply, then again, white's 2nd move is illegal.

I posted the game via pictures in #23.

Is there any position I show there that you disagree with?

Yeah, I think I got mixed up...

For some reason I thought that the piece on c7 was a knight on black's turn and becomes a bishop on white's move. But that doesn't make any sense, sorry about that. I keep changing the rules in my head I guess haha.

Yeah, I was trying to apply the rule "(only) your pieces change with your half move" but I messed up at the end.

So then black could play ...Kd8? If Bxc7 turns the bishop into a knight at that point, then ...Kd8 is just going diagonal to the knight which is perfectly safe.

I mean... it's true that Magnus could play h3 or something and put black into check, since now the piece on c7 would be a bishop, checking black, but obviously it wouldn't be mate, as black could just take on c7 for example, right?

So I'm still not sure how Magnus is claiming mate. Are you? It seems like no matter which rules you use, an inconsistency pops up, but I could easily be missing something so who knows.

Soon you guys are turning to page three. The warning about the 20 point IQ drop has never been more pertinent!

Molecular level clusters of green jelly are already starting to form in the corners and in the edges of your brains... watch out!

Twenty posts from here you'll already be capable of shaking your heads and hearing a slight "whoosh" from the inside...

Doing logic makes you dumber?

I decided to keep my IQ level steady already at the top of the current page - cutting my losses thereby. 

Yeah lol you didn't even take your own advice :)

No, I don't think it's mate. I think either Carlsen is trolling, or as he said, he's new to the game so he didn't notice c7 could be captured.

I think it's worth pointing out this could be a real variant though. Because if c7 can't be taken, then he could claim mate by revealing a few different kinds of rules... I think the simplest is the rule: "the square a pieced moved from is always attacked by that piece." This is true in normal chess (except for pawns) so it wouldn't be too difficult to remember.