“Five Easy Pieces” problem

I’ve posted on the Retros mailing list, December 27^th, 2009, this “problem with an incomplete diagram” (please forgive again my bad English):

> Hello RetroFans,

16+16 C+(Euclide)

Remove 5 white pieces that are placed

on same-colour squares and reach the new

position in 11.0 moves.

(example of a possible removal : Ra1,

b2, Bc1, d2 and f2, were on dark squares)

11+16

Which are the 5 white pieces you'll

have to remove from the chessboard in

order to complete the above task?

Best,

É.

---

The answer is further down.

Remove Nb1, Qd1, e2, Bf1, g2

11+16

This position can be reached in 11.0 moves (the path is NOT unique):

(1)e4 c6 (2)Ba6 NxB (3)Qf3 Nb8 (4)Qf6 exQ (5)e5 Bd6 (6)Nc3 Bc7 (7)Ne4 d6 (8)g4 Bxg4 (9)Ng5 Bh5 (10)e6 fxe6 (11)Nf7 BxN

I guess this is the only removal of Five-White-Pieces-of-the-same-colour-square allowing the players to achieve the task.

Best,

É.

_________

Nicolas Dupont mentions this pb here (in French):

http://www.france-echecs.com/index.php?mode=showComment&art=20091228181321915

I’ve received this nice comment from Mario R. on December 29^th 2009:

> Your new challenge "Five White pieces, same square-colour" was also interesting.

It shows an unusual asymmetric effect: on white squares, you have the choice between 8 pieces, on dark squares only between 7 pieces.

Furthermore, on dark squares, the removal of pawns might expose the wK to diagonal checks, while on white squares this is not possible (of course only if the wK doesn't move).

>> I guess this is the only removal of Five-White-Pieces-of-the-same-colour-square

>> allowing the players to achieve the task.

There is no need for guess work here: there are only 56+21 positions to investigate, and that's not really a hurdle for 'natch' or 'Euclide'.

I used the latter to validate, that only the removal of (Pe2,Pg2,Nb1,Qd1,Bf1) fulfills the conditions of the stipulation.

So you can mark your problem as "C+" (Euclide).

Thanks, Mario -- done!