[Retros] FEN fun

Eric Angelini Eric.Angelini at kntv.be
Thu Aug 1 10:59:21 EDT 2013

Waow, thanks François !
Fun with FEN tonight !

De : retros-bounces at janko.at [mailto:retros-bounces at janko.at] De la part de Francois Labelle
Envoyé : jeudi 1 août 2013 16:54
À : The Retrograde Analysis Mailing List
Objet : Re: [Retros] FEN fun

Hi all,
Below are FEN problems with a unique solution.

"Find a game reaching a position with the given multiset of FEN digits"

1111222888 in 2.5 moves (2 captures)

1111223888 in 3.0 moves (3 captures)
1112225588 in 3.0 moves (3 captures)
113334488 in 3.0 moves (3 captures)

11123344456 in 3.5 moves (2 captures)
11226888 in 3.5 moves (4 captures)
12234888 in 3.5 moves (4 captures)
1227888 in 3.5 moves (4 captures)
123333488 in 3.5 moves (3 captures)

111112225668 in 4.0 moves (4 captures)
11112223888 in 4.0 moves (5 captures)
112222333366 in 4.0 moves (2 captures)
11222233488 in 4.0 moves (4 captures)
112226688 in 4.0 moves (4 captures)
12226788 in 4.0 moves (4 captures)
12235888 in 4.0 moves (5 captures)
12334888 in 4.0 moves (5 captures)
1237888 in 4.0 moves (5 captures)
2222334477 in 4.0 moves (4 captures)
222233778 in 4.0 moves (4 captures)

The number of captures is implied by the FEN digits (it is the sum minus 32), so I report it to save you the effort.

I think that the first problem is worth solving (being the shortest problem of this type). Then it's up to you if you want to solve more. Note that I'm blindly giving the exhaustive list of such problems up to 4.0 moves, so some of the solutions are very similar. For publication it would be better to make an editorial selection and pick only one problem for each "idea".

I'll post the solutions in one week.


On 07/30/2013 04:47 AM, Eric Angelini wrote:

Hello Retro-fans,
here is a 5-minute puzzle for the August break.

It is possible to reach, after Black's third move,
many positions having a FEN format where all numbers are prime.
Find a game where the last move was _not_ a pawn move.
(The solution is far from being unique -- but the "trick" yes,
I hope.)


(BTW, does this open a new kind of chess problems -- I mean,
playing with the FEN notation -- or is it, as I imagine, old hat?)


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