Would you say #5893 is a better example of a position with multiple distinct solutions?
Yes, that's a more clear-cut example, with different starting moves and notable changes, especially the original vs promoted knight on b8. Quite a stroke of luck that the second solution was unintended!
I guess I will now have to study the 4 (or are there 3?) solutions in order to react but obviously Euclide will not approve of 4 proof games when there are countless alternatives as was suggested. When the 4 proof games are really the only ones - with the themes as described - it's a perfect SPG challenge - as I wrote from the beginning. Move sets are irrelelevant but obviously the proof games should be as different as possible - especially the starting moves. Once the first moves diverge that commonly happens naturally for the remainder.
Unfortunately I have no proof game solver and decided to rely on your texts. Not that accurate I conclude.
Btw - as Rocky wrote - the retro-community commonly refers to proof games as unique move sequences for this type of challenge - but that is precisely what is different for this whole topic. Almost 100% of the content here is about (shortest) proof games which are not unique which means that all of you need to be very precise when making distinctions and exceptions in your texts. Btw2, there are other places in the retro-domain where the concept "proof game" means just that - without uniqueness. Uniqueness is only associated with "shortest proof games" - but not in this topic on chess.com.
I guess I will now have to study the 4 (or are there 3?) solutions in order to react...
Uniqueness is only associated with "shortest proof games" - but not in this topic on chess.com.
Are there 4 solutions, or only 3? #5905 doesn't leave me with any doubt about this.
I think it's a good thing that uniqueness doesn't have to be only associated with SPGs in this topic. That would rule out interesting questions like the one discussed here a while back on positions that have more than one SPG and a longer proof game that is unique.
I've just checked on the Schwalbe database and found a PG in 8.0 moves where the stipulation is "2 solutions, each with 2 variations".
It would be interesting to know Euclide's verdict on this position. The output from Stelvio 1.6 says "Found 4 solutions. The problem is correct. Solving time: 00:00:01 seconds."
Apparently it makes no distinction between solutions based on their starting moves.
Ah yes, there were many posts on it, starting with #5895! In the world of composition SPGs are only associated with uniqueness - but with a twist as Rocky and I indicated. When you differentiate them on a theme there may be a unique SPG associated which each one of the thematic options (like a common problem may have 4 variations for the AUW promotions). Without such a theme they are merely a set of extra "bad luck" SPG's.
The problem is that on this site SPG's also refer to non-unique SPGs and from Leither's language on move collections - which do not matter - and without reference to a theme. I could only deduce that he had constructed some set of random proof game solutions. Had he used Rocky's language, it would have been clear straight away. So there was a miscommunication. I probably could have resolved it by finding the 4 solutions myself (or seeing #5905) but I didn't want to waste the time on what looked like a sloppy challenge and commented on the "move collections" in the text.
Btw, I wrote "4 (or 3)" only because someone mentioned 3 somewhere and it didn't matter for the issue. To prevent someone shouting "there were 3!".
I knew and accept that you use the term SPG different from the retro-community but that will also open the door to the occasional misinterpretation when it is about text rather than just diagrams. Never know how many SPG's you will find inside a post! 
Just quickly checked the 4 solutions in #5905 and concluded the quartet does not pass the composition test for forking proof games. Almost always they fork on the first move (that's why it's hard to make 3 or 4) unless there is some justification for delaying it. I have never seen one but there always are when you have a "good storyline"
. I recall having seen an A-to-B proof game which does not start on game move 1 but that takes us further from home as does every new condition or complication.
Of course, I had acknowledged that the challenge was sloppy shortly after posting the position, so here's a challenge that isn't. Can anyone here construct a position with at least 2 unique solutions that differ from move 1?
Of course, I had acknowledged that the challenge was sloppy shortly after posting the position, so here's a challenge that isn't. Can anyone construct a position with at least 2 unique solutions that differ from move 1?
Did you mean in addition to the one already mentioned by Rocky which has four solutions with two different starting moves, and the one you constructed at #5889?
Can anyone construct a position with at least 2 unique solutions that differ from move 1?
Yes, a number a people can do it. Here's a short one constructed by François Labelle.
Proof game in 5.0.
I think Leither wants us to engage our workbench rather than consult our encyclopedias.
I think Leither wants us to engage our workbench rather than consult our encyclopedias.
I think so too, but he didn't word his question as a challenge. If he had said "you" instead of "anyone", it would be a challenge. (And I wanted to show the one from Labelle, since I think it's neat.)
I think so too, but he didn't word his question as a challenge. If he had said "you" instead of "anyone", it would be a challenge. (And I wanted to show the one from Labelle, since I think it's neat.)
Yes, it's lovely! Rocky's 2x2 is good as well but a bit technical. Labelle's is more pleasing to the eye.
I've just checked on the Schwalbe database and found a PG in 8.0 moves where the stipulation is "2 solutions, each with 2 variations".
It would be interesting to know Euclide's verdict on this position. The output from Stelvio 1.6 says "Found 4 solutions. The problem is correct. Solving time: 00:00:01 seconds."
Apparently it makes no distinction between solutions based on their starting moves.
Euclide also considers it sound with 4 distinct solutions. I didn't test it because I saw the "C+" next to the diagram on the database. Looking at that page again, it actually mentions the software used was Euclide!
I still haven't tried Stelvio, even though when I googled it I learned that it's supposed to be much faster than Euclide. Maybe I'll check it out and cover it as a blog topic.
I still haven't tried Stelvio, even though when I googled it I learned that it's supposed to be much faster than Euclide. Maybe I'll check it out and cover it as a blog topic.
When you do, here's a problem you may want to check out. I saw a report of Euclide solving it in about 5 hours. Stelvio solves it in 8 seconds.
rn4n1/p7/bpppKpp1/k1r1p1qp/7b/5P1P/PPPPP1P1/RNBQ1BNR
36
P.S. I just found it at P1004103, where it says Natch solved it in 40 seconds, so the report on Euclide might be wrong.
Here's a short one constructed by François Labelle.
Proof game in 5.0.
That's a nice one. Labelle is a problemist/programmer who discovered the only known unique proof game that ends with just the two kings left on the board. An amazing task! Guess how much computer time was required to find this game? See my blog for the answer!
Labelle is a problemist/programmer who discovered the only known unique proof game that ends with just the two kings left on the board. An amazing task! Guess how much computer time was required to find this game? See my blog for the answer!
That's amazing indeed! I recall Andrew Buchanan mentioning that no such proof game existed for the complete massacre task yet but I suppose this is a rather recent one [edit: 2012 is not that recent but Andrew and I go a long way back]. It even conquered the final obstacle of a dead position before the last move(s) by leaving a pawn (even 2) till the end. I wonder if that was one of Labelle's conditions or that was sheer luck!
The next challenge is the Holy Grail960. With any luck, in a few years time, you can place 2 kings on an empty board and tell the contestants that the position was reached after 18.0 moves. Then you ask them to determine what the Chess960 setup position was. Solving time: 20 minutes. Start: NOW
what about this?
When proof game composers honor different shortest proof games for the same position they do that on the basis of another attribute. Like, there is 0-0 in one proof game, and 0-0-0 in the second one.
I would like to honor Leither's position, since it has exactly four SPGs, one without castling, one with castling by White, one with castling by Black, and one with castling by both sides.
Actually I haven't studied Leither's 4 proof games - I reacted on the general concept of proof games where the move order doesn't matter which was in Leither's original post on this. Which is apparently not what he intended. If what n9531l1 says is true than we'd have 4 SPG's separable by an "attribute" or "theme", something the composing community would applaud. But apparently that is not true either. So I can only conclude that within the themes are many more proof games honoring the theme and the length but not the move set. For instance there might be a 1000 proof games without castling and for just one move set there happens to be one move order.
again, for all these 1000 proof games there must be one move set for each, and each of the move sets must have one move order
this sort of choosing shouldnt be possible either, according to my understanding
but just leave it
All the other 999 proof games without castling exist as well but they contain some moves which can be reordered. Can someone explain how I could ever find the one with one move order and reject the other 999? Then I would have to assess all 1000 proof games, right? And I would have to be sure there is no other move set which features just once among the remaining 999. How do you explain this to any solver?
To be clear, it is different when there are not 1000 but just 1 shortest proof game for each theme. That would be great!