Shortest-proof-game challenge

39 moves, I'd be surpised if someone improved this one.

They are both the same!

Hey guys, just looked at this thread and remembered seeing it a long time ago when it was just created. A lot of really good stuff here, I like these kind of retro problems in the forum.

browni, nice solution, but the problem here is that you go for 2 promotions for each side. The extra pawn moves cost you, each side can do with just 1 promotion.

Here is a 35.5 move solution:

I believe this is the fastest. Here is my analyse:

First of all, the symmetry (as always) makes it a bit more convenient to solve.

The knights have to be captured first to free up the bishops and the game. This is their most efficient route (6 total).

Next, for the bishops, the route they take is also the most efficient to be taken by one of the pawns (4 moves total).

Now we need to plan ahead. One of the a pawns have to be captured, and one of the h pawns (of opposite color) must be captured, to let each side promote a new piece to be taken by one of the pawns.

At first, my strategy was to capture those pawns with the queens, and I was able to reach a 36 move solution. Later I realized that the kings themselves, on the way towards their final position, can capture these pawns, which saved me half a move.

So the queens get into their positions to be taken by the pawns. This takes a minimum of 2 moves total. If the white queen could get to e5 in just two moves (or alternatively, if a newly promoted queen on a8 could reach e5 in just two moves) a 35 move solution would have been possible. But it is impossible as far as I can see.

One final trick is that white can castle long, which saves him a move. The final sequence is pretty much straight forward.

I didn't think to have the king capture the pawns, nice job!

I'm sorry shoopi, but I've come up with a better solution. Even  though you haven't technically beaten me here, you have the way I see it.

There is no need to be sorry, this is great. I didn't consider waiting with the original queen before promoting to a new one. Nice final touch to solve that problem and reducing the solution by half a move.

Just goes to show that these things are really nice and very innovative, there are many things to consider and surprises lurk in every corner.

I'm fairly certain that this is the best possible. So I suppose you're next to post a diagram!

lets check it mathmatically

I think it is optimal though

It is optimal.

 The knights have to be taken first - on c3/f3/c6/f6. While it is possible to sac just one knight for each side and use the bishops for the other pawn captures (instead of a second knight), it is extremely wasteful and inefficient.

Therefore, knights take a minimum of 6 moves total (3 for each knight).

Next for the bishops, a minimum of 4 moves total to be captured (2 for each bishop).

Queens - minimum of 2 moves total to be captured.

Kings - it takes a minimum of 6 moves for black to reach f2 and 7 moves for white to reach c7. However white, by castling long, saves a move getting his rook to d1.

So it takes black 2 moves to get his rooks to final position, and just 1 move for white to get his rooks to final position - 8 moves total for kings and rooks.

The pawns needed to be captured are captured within the kings journey to their final position, but it takes at least one move in order to bring them close enough (no way to capture those pawns withought using at least one move).

It takes 5 moves for the a and h pawns to promote.

The promoted pieces on a8 / h8 would take at least 2 moves to be captured by a pawn.

Finally, the pawn captures themselves take 6 moves total.

Total: 6 (knights) + 4  (bishops)+ 2 (queens) + 8 (kings and rooks) + 1 (pawns needed to be captured) + 5 (promoting) +2 (promoted pieces) + 6 (pawn captures) = 34 full moves, as per browni's sequence.

So browni, are you going to post the next diagram?

I also agree that this is a good idea to keep the thread somewhat flowing.

 I think that 3 days (72 hours) is more than enough time for the solver to post a new diagram.

And in the case he hasn't and the time limit has passed, anyone who is interested can post a valid diagram (or challenge) for others to solve.

I will post a diagram. I'd like to come up with something good, but I've got a lot to do so that might not happen. Give me a day and I'll come up with something.

No problem.

And off the record, it doesn't have to be something "really good". In fact, if you look at many of the problems posted here - such as the last one - the poster didn't even have a solution, yet they ended up being fantastic exercises!

heck I have one that I am waiting to try. it is really good.

One note - If the poster doesn't have a solution, then they can try it too.

I would like to add the stipulation that white may still legally castle both ways from the final position.

I hope this position is reachable and that I didn't mess up.

According to my calculations, the theoretical minimum of moves it would take to reach this position is 42.5 moves (I.E. white's last move is labeled 43).

Surprisingly, after trying it out I managed to do it. So I'll just wait a little while before posting it to see where's the competition at, and whether anyone manages to tie me (or god forbid surpass me, but I don't think that's possible).

I'll just go ahead and post my solution:

Here is my analyse:

Black needs to make a lot more moves than white to reach the final position. So we don't really care for white moving efficiently, but black must move at maximum efficiency.

Looking at the board we can see that white must have made at least 15 captures, which account for all of black's missing pieces. These captures were made inside the triangle from a7 to a3 to e3. In order to calculate the theoretical minimum number of moves, we need to check the minimum number of moves it takes for each black piece to reach this "capture zone" (save for the king which must get to a8).

When we go through each piece individually, it is quite simple to calculate. But there are a few special cases we must look at. For instance, it would take the b8 knight just one move to get to the triangle (a6 square). It would also take the c8 bishop just one move to get to the triangle, but it relies on the same a6 square. So, between the two pieces you must actually make at least 3 moves total. Also, the pawn on a7 shouldn't move at all, since it is already in the triangle, and the rook on a8 will get to d8 after black castles long (which he should), then it would need just 1 move to get to the triangle as well. Finally, black must promote f7, g7 and h7 pawns. But the pawns cannot promote on h1 square (because the rook must stay there the whole time), or e1 square (because of the king) and cannot go through f2 square, which would put the king in check. The pawns may pass through white's pawns by capturing white's 4 absent minor pieces. As it turns out, all three pawns must promote on g1 and it would take exactly 4 captures to achieve it. Finally, after promoting, it would take at least two more moves to get to the triangle. You can check it out yourself to see that you understand why.

The calculation for each piece goes as follows:

a8 rook - 1

b8 knight - 1

c8 bishop - 2

queen - 1

king - 3

f8 bishop - 1

g8 knight - 3

h8 rook - 2

a7 pawn - 0

b7 pawn -1

c7 pawn - 1

d7 pawn - 2

e7 pawn - 3

f7 pawn - 7

g7 pawn - 7

h7 pawn - 7

Total: 42 moves.

The position must be reached with black to move, which is why it must take 42.5 moves.

If this is accepted, I will go ahead and post the next position (though don't expect anything exceptional).

I can't find any flaw in your solution. I don't like how fast paced this is. I think we should try to come up with harder problems, but it's often hard to know how difficult your problem will be until someone else tries to do it.

I have learned a little bit from this one though and have ideas on how to make the next one more difficult.

I agree, it is hard to come up with challenging and unique positions (although, I think your last position was quite good. I enjoyed it). But, while challenge and innovation is fun, I'm not really afraid of faster paced, so-called easier ones. They contribute to the flow of the thread and participation of more players. If this thread was in the "more puzzles" forum I suspect it would have been even better.

Regarding your ideas for future positions - great. Looking forward to it

Anyway, here's a position I assembled rather quickly. I hope it is not too easy for your taste, I assume it is quite easy, since the game is still young.

It started in the more-puzzles forum, look at the address.