13 Nov 06
Originally posted by DarrieI think the answer is correct!
That position cant be legal in my humble opinion. The only way for the King to get to a2 is via the back rank, but then the rook cant get to b1, since the last move must have been Kc1. Where is my thinking error?
My first solution was this:
The problem here is, that I cannot tell what the position before was. I only know the king moved from d8 to c8 but I don't know which piece it took there (or if he took a piece at all). This is covered in BigDoggs answer: There must have been a knight on c1, because that is the only piece that can get there in the move before White's last move. It could not have been unoccupied because then it really seems to be an illegal position as you pointed out.
13 Nov 06
1 edit
Originally posted by David113Edit: David113 cooked my first try by -1.Kd1-c1 Ka1-a2 -2.Rc1x~b1+ etc.
BDP's solution is not correct. Do you see why?
Good spot. I noticed that Pa3 is serving no useful purpose in my first try. I can make better use of that 7th unit to jam the a1 square, which (I believe!) saves my idea:
13 Nov 06
Originally posted by BigDoggProblemThe bishop can only have got there through promotion, and the king cannot have moved to a2 afterwards so that position is impossible.
Good spot. I noticed that Pa3 is serving no useful purpose in my solution. I can make better use of that 7th unit to jam the a1 square, which (I believe!) saves my idea:
[fen]8/8/8/8/8/8/kPPP4/bRK5 w - - 0 1[/fen]
Does this work?
13 Nov 06
2 edits
I think BDP's second solution is fine. The bishop promoted on a1. Then the black king came to a2 from b1. then the white rook came to b1, the white king came to d1 and the black knight came to c1. Anyway, if you don't like the black bishop on a1 you can replace it by a white knight.