Can it be done?

well. to give a last minute attempt.

the pawn on b3 probably comes from f file.

the 2 white pawns have probably promoted to allow 2 captures for black.

white needs some captures, but theres plenty of black pieces for that.

hmm so far im not getting it. Im guesing its legal, but its all about king manuevers and how other pieces affect it right? I shall have a go =P

yes by moving thep ieces around on the board the lazy way, or perhaps the harder way, I have got into the position where both kings cannot meet each other. Sorry cobra but i just cant be bothered to work out the precise piece manuevers BEFOREHAND because I cant be bothered to think and im not as hardcore :D

Obviously the kings must arrive in some way before the other pieces and probably pawns get into their positions.

hmmm.... =P solution please :D Ill just flick through it and go oh so thats how it was x(

THERES 3 NEW COMMENTS COBRA TIME TO READ UP INCASE THERES AN ANSWER ;D
all from one person and theres no good attempt =((

Sorry about the long (yeah, I know - REALLY long) delay; I've been having problems with my internet connection for the last couple of days, which I only just managed to fix about an hour ago.

Well, anyway... I actually decided to just give part of the solution, with the intention of jumpstarting the people who may be stuck or have just given up on it. So, just read through this, and then try to finish the puzzle!

(1.) The best way to approach this problem is to consider how the White king reached d6. More specifically, what square did the White king occupy immediately before "arriving" (i.e. moving for the final time) on d6?  For the sake of being thorough, let's list all 8 squares surrounding d6 as possibilities (since they are all 1 king move away from the target square) : c7, d7, e7, e6, e5, d5, c5, c6

(2.) The White king clearly did not arrive from d7, because the Black pawn on d7 has occupied this square throughout the entire game. Note also that this same pawn has controlled c6 and e6 since the very beginning of the game, so the White king could never have accessed these squares without moving into check. We are now left with 5 possible squares from which White's king arrived: c7, e7, e5, d5, c5

(3.) Consider the Black bishop on f8. It began the game there, but could have left and returned at any time. However, note that it could only have done this via the a3-f8 diagonal (the unmoved g7 pawn has been blocking the shorter diagonal since move 1), which means that if White's king arrived before the bishop on f8, then it would be impossible for Black's bishop to get to f8 without either jumping over the king, or White ignoring a check (on the move before Be7-f8). Therefore, Black's bishop "arrived" on f8 before The White king on d6.

(4.) From (3), when White played Kd6 (for the final time), the Black bishop was on f8, so there must already have been something on e7 to shield the king (otherwise, it would be moving into check). This makes it obvious that the king could not have arrived from e7. This leaves 4 possibilities: c7, e5, d5, c5

I'll wait a day or two to see whether anyone can take it from there...

No takers? All right - then here's the next part of the solution. Continued from previous post:

(5.) The pawn on f6 came from f7 (The analysis that proves this can be found in (19), but for convenience it will not be explained at the moment.), so it must have arrived before the White rook on f7. Furthermore, the presence of this pawn prevented the f7 rook's arrival from f6 (or f5, or f4, etc.), while the unmoved g7 pawn made it impossible for the f7 rook to arrive from g7 (or h7). This means that White's rook must have arrived from either e7 or f8.

(6.) If the White king arrived from e5, then it must have done so either before the arrival of Black's f6 pawn, or on the move immediately after f6+ was played. From (5), f6 came before Rf7, so this would mean that White's king arrived before his rook on f7. From (3), Bf8 came before Kd6, so Black's dark-square bishop was already glued to f8 when the f7 rook arrived, meaning the rook couldn't have arrived from f8. Also, since we've established that both Bf8 and Kd6 came before Rf7, it is evident that the move Re7-f7 would illegally expose the White king to check. But from (5), the f7 rook could only have arrived from either e7 or f8. Thus, our hypothetical scenario in which the White king arrived from e5 is impossible. Continuing from (4), then, the possible squares from which White's king arrived are: c7, d5, c5

I'll wait a couple more days to give people a chance to capitalize on the new information and complete the solution themselves; hopefully, there's still some devoted solvers out there

and some more days cobra eh :P ill help bump this topic up.

that is deep analysis, or maybe its just because im not taking it in lol. Reading it on the surface without the diagram = *puff!*

It's finally here: the next part of the solution!   Been too busy with other stuff for a while now, and am starting to lose interest in this sort of thing. Didn't want to leave the explanation unfinished, though... so, better late than never. Before reading this, however, you may want to [re]read post #24 and post #25 (as well as possibly opening up a separate window to view the position from). Well, here goes nothing:

(7.) The White king could easily have arrived from c5 or d5. It is important to note, however, that this could only have happened prior to the arrival of Black's king on c4 (or else one of the kings would have had to illegally move "within range" of the opposing king).

(8.) Because of the unmoved Black pawn on a7, White's a8 rook could not have arrived from anywhere along the a-file. So, it arrived from b8 (or c8, d8, etc.), meaning that Ra8 came before Qb8. This, in turn, means the Black queen did not arrive from a8. Also, the unmoved pawns on a7 and b7 make it impossible for Black's queen to have arrived from a7 or b7 (or any square along the b-file), so it must have come via either the h2-b8 diagonal or the c8-h8 portion of the 8th rank. 

(9.) If the White king arrived from c7 (it gets a bit confusing here; keep in mind that all logic in this "number" is conditional, and based on this assumption that White's king arrived from c7), it must have done so before the Black queen's arrival on b8 (since with the queen on b8, the move Kc7-d6 illegally ignores a check). With the king permanently on d6, Black's queen could not reach b8 via the h2-b8 diagonal (without either jumping over the king, or having White ignore a check on the move before Qc7-b8), so from (8) it would have to have arrived from c8-h8. This means that both Qb8 and Kd6 must have come before Nc8, in this scenario. So the knight on c8 arrived from either b6 or e7. Recall that from (3), Bf8 preceded Kd6; therefore, the move Ne7-c8 would illegally expose White's king to check in this case, leaving b6 as the only square from which the White knight in question could have arrived. But if Black's king arrived on c4 before any of this, it would imply that before Nb6-c8 Black was in check with White moving.

(10.) From (9) it is clear that if the White king arrived on d6 from c7, then the arrivals of the Black king, Black queen, White king, and White knight followed the order Kd6, Qb8, Nc8, Kc4 (what's important is that White's king had to have arrived before Black's). Now, from (7) the White king's arrival must also have preceded that of the Black king if White's king came from c5 or d5, and from (6) the only possible squares from which White's king could have arrived are c7, d5, and c5. Thus, we can conclude with certainty that the White king arrived before the Black king.

There's still a great deal more analysis to this puzzle, but more of it will [definitely] come tomorrow (in fact, by Wednesday the entire solution should be up). If anyone comes up with anything new before then, you're welcome to post it, though of course after all this time I seriously doubt anyone is still interested :( 

Continued from post #28:

(11.) Consider the square from which the Black king arrived on c4. Since the White pawns on b2 and c2 have never moved, the Black king wouldn't have been able to access b3, c3, or d3 at any point during the game. That leaves only b4, b5, c5, d5, and d4 as possibilities.

(12.) Since Black is mated by a double check in the final position, the last move was clearly Nb5-a3#. With the unmoved pawn on b7, it is clear that Ba6 came before Nb5, as well as before Kc4. This means the Black king couldn't have come from b5 (since with White's bishop on a6, the move Kb5-c4 ignores a check). From (11) that means Black's king arrived from either b4, c5, d5, or d4.

(13.) From (10) Kd6 definitely came before Kc4, so if Black's king arrived from either c5 or d5 then the two kings were mutually checking each other at some point (impossible). We are now left with just b4 and d4 as possible pre-arrival squares for the Black king.

(14.) Both b4 and d4 are controlled (in the final position) by the White pawn on c3, so regardless of which of these squares the Black king arrived from, it must have come either prior to the arrival of this pawn or on the move immediately afterward (as in dxc3+ Kc4). Now, before the White pawn was on c3, it was obviously on d2, where it would be blocking White's dark-square bishop. Notice that with the b2 pawn never having moved, the aforementioned bishop could not have left c1 prior to dxc3 by White. This would imply that when Black's king arrived on c4, the White dark-square bishop had not yet arrived on c7 (in fact, it was still on c1 where it began the game!).

(15.) The Black queen arrived on b8 either before or after White's king on d6 (it doesn't really get more obvious than that, does it? ). From (10) White's king arrived before his Black counterpart, so if Qb8 came before Kd6 it also came before Kc4. If Black's queen arrived after the White king, then from (9) it arrived before Nc8, which preceded Kc4; clearly Qb8 must have come prior to Kc4 in this case as well. This allows us to confirm that the Black queen arrived before Black's king (because this is true in both of the above cases). Since from (14) Kc4 came before Bc7, it follows that the Black queen's arrival also preceded Bc7. Similarly, White's king must also have arrived before Bc7 because from (10) he arrived before the Black king. So at some point the king was on d6 while the queen was on b8 but the bishop was NOT on c7. This implies that, during this time, the king was shielded by some other piece, which occupied c7 before the bishop.

I'll post more tomorrow... unless somebody comes up with something before then.  

Continued from post #29:

(16.) The piece occupying c7 before the bishop, as described in (15), could not have been a White piece. If it were, it would be permanently pinned after Qb8 and Kd6, and therefore would be unable to vacate the c7 square for White's bishop. It also was not a Black pawn, bishop, or queen for a number of obvious reasons (namely, that any of these pieces would threaten the king on d6). So before the arrival of the bishop, the White king was protected by either a Black rook or a Black knight.

(17.) Black has 11 remaining pieces in the final position, so White has made a total of 5 captures during the game. To be more exact, Black is missing a pawn, a rook, two knights, and a bishop. Looking at White's pawns, it is clear that White made the captures axb and dxc at some point, accounting for 2 of the 5 captures. Furthermore, the unmoved pawns on b7 and d7 indicate that Black's light-square bishop never moved from c8. This means that it was captured specifically on c8, which accounts for a separate 3rd capture by White.

(18.) White has 14 remaining pieces, meaning Black has captured only twice. Clearly, one of these captures was cxb. The only pieces missing from White's army are pawns. Since b4 comes from a2, c3 from d2, and e3 from e2, the g and h-pawns are the ones that were taken. So, one of these pawns was captured cxb, which can only be explained by a pawn promotion. The g-pawn, however, would need at least 1 capture to promote, while the h-pawn would need at least 2. From (17) White also captured axb and dxc, as well as the bishop on c8, so to promote both pawns White would need an impossible total of 6 captures. Thus, exactly 1 White pawn promoted during the game.

(19.) Since from (18) the only promoted White pawn was captured cxb, it would have been impossible for Black's e-pawn or f-pawn to change files. This means that the pawn on f6 comes from f7 (this is a relevant fact in section (5), found in post #25) , and that Black's missing pawn began on (and remained on) the e-file. This is rather important, because with White's e-pawn (now on e3) blocking the file throughout the entire game, it implies the missing Black pawn did not promote, and so it must have been captured on the e-file. Now, from (17) White captured axb, dxc, and on c8 (the trapped bishop); adding Black's unpromoted e-pawn brings the capture count to 4. From (18) we must add either 1 or 2 to this total so as to account for a pawn promotion (of either White's g-pawn or h-pawn, respectively) - adding 2 brings the total to 6 captures by White, exceeding the number of missing Black pieces. It was therefore the g-pawn that promoted, using a 5th capture to reach either the f or h-file. And with no other captures available to White, it follows that Black must have taken the h-pawn on its starting file. One final thing to note is that after promoting, the new piece may have been captured cxb OR replaced the piece that was captured cxb.

The next part of this analysis is quite complicated, and pretty tough to explain thoroughly (not to mention time-consuming)... so I'd certainly appreciate it if at least a few people would have a look at this and fill in some of the blanks. Thanks in advance  

cobra bump <3

more new comments to get your hopes up no? :O

bringing diagram to page 2:

Summary of post 30:
16) before the arrival of the bishop, the White king was protected by either a Black rook or a Black knight.

17) Black's light squared bishop was captured on c8 (accounting for 1 capture from white)

18) 1 White pawn promoted during the game, which was the g pawn. This makes up for the needed piece to be captured on b3 (since the capture on b3 was not a pawn)

Have fun :P

 I'm actually quite doubtful that anything could get my hopes up at this point... well, at least you got a few member points out of it anyway 

Not a bad summary, but you skipped over (19)  ; )  At least you read and understood most of what was said in that post, though.  Btw, have you also been following the previous parts of my analysis (posts #24-29) ?  Maybe you could sum up a bit of the info from those as well, eh?  = P

well no. 19 is summarised in no.18 a bit, but maybe there may be some more i missed as i didnt actually follow it (without looking at the diagram and stuff AT ALL, its impossible). Maybe some of that there is key to solving the rest? :P I only put the main points, skipping out "why", but then that "why" could be used again later on but mmm so i dont think i missed 19? Unless i missed a mainpoint.

So, I was recently curious again with the fate of this unsolved (mythical?) puzzle by cobra.

I remember a long time ago, cobra asked me to take a look at this and try to solve it. Also, since he had mentioned a few times that he might "post the solution", I always had the impression that this position was legal and must have a spectacular solution (which wouldn't surprise me considering cobra's skills).

I just now tried to tackle this one seriously, sitting on it for like 3 hours, when it finally occurred to me that I can only come to the conclusion that this is impossible. Following that, I started reading cobra's "parts of the solution", which then, gradually, made it even more apparent to me that the position is in fact illegal.

With that in mind, I will now attempt to complete cobra's analysis of this position, and prove that this position is illegal. I doubt that I will be as thorough or as systematic as cobra, but I believe that I will cover pretty much all of it.

First, a very short summary of some of the important points thus far:

1) White has promoted exactly one piece (the g pawn).

2) Before the black king arrived at c4 for the final time, the white king was already on d6, the black bishop on f8 (and another piece on e7), the black queen on b8 (and another piece on c7), and the white knight on c8.

3) After white played dxc3, the black king must have already been on c4, or go there immediately after white plays it (dxc3+ Kc4).

If it hasn't been covered before, then the reason for this is that we already know the white king arrived before black's, so d5 and c5 squares are not available. If the white bishop was already on a6, then b5 square is not available, and if it wasn't, it would have no way of getting there after the black king is on c4, since it could only get there via the a6-f1 diagonal.

4) from points (2) and (3) we can conclude with certainty that after white played dxc3, both the a8 and the f7 rooks were already in their final position. Otherwise they would have no way of getting there. This is a critical point.

Now, white's h1 rook has no problem of getting to either one of these squares. But the same is not true regarding the a1 rook. There are only two possibilities - he got out of a1 after dxc3 and the release of the c1 bishop, or through axb when he can get out from the a file.

Finally, from here, we have but three plausible tries (hopefuly I haven't missed any other reasonable tries) to attempt to reach the final position. These tries revolve around the promoted g pawn.

Scenario one:

The promoted g pawn was used for cxb. This means that white must play axb before dxc3 to free his a1 rook - because of (4). In this scenario, there must be a white pawn on b4 and a black pawn on b3 before the black king arrived at c4 for the final time, otherwise the black pawn would have no way of getting to b3.

So far in this scenario, black has captured white's promoted pawn (cxb), and white has captured 2 black pieces out of the 3 available (to allow the g pawn to promote and for axb). The final piece must be used for dxc3 which will free the c1 bishop, but now we have a problem - we are missing a piece to block the check from either the b8 queen or the f8 bishop. Notice that the white knight on a3 cannot be used for this, since at this point he is on b5 blocking the check from the a6 bishop. Also note that we want the c1 bishop to reach c7 square, so the only way to attempt this is by using another black piece to block the check on c7 - which can only be the rook on d8. But in this case, the rook would have no way of reaching d8.

Illustration:

 Scenario two:

The g pawn promoted to a bishop on f8, and was eventually placed on c7. In this scenario, as in the previous one, white also must play axb to get his rook out before dxc3 because of (4). Here, the c1 bishop must be used for black to play cxb, but as we will see, this is also impossible.

Illustration:

So, I was wrong thinking the position is illegal. Turns out there is another "reasonable try" to reach the position.

Scenario four:

The g pawn promoted to a queen and got to e7. I just didn't consider this for some reason. The only problem is that black is seriously short on moves - he has his h pawn, his e pawn, and another piece on c7 blocking the check from the queen - either a rook or a knight.

However, in order for the final sequence to be possible, white must play g6xh7 to just make it to the final position in time. But if white captures a knight on h7, what could have been black's last move? where did the knight come from? f8 and f6 are blocked. That leaves g5, but there is currently a white pawn there.

Can a rook make it? well, the answer is yes.