[Retros] Illegal moves by grandmasters

[Francois Labelle]

In June 2007, Noam Elkies posted to this list about an illegal move (due
to Article 1.3 of the Laws of Chess) in the game

Shakhriyar Mamedyarov (2757) vs Viswanathan Anand (2786), Dortmund, 2007
http://www.chessgames.com/perl/chessgame?gid=1464708

Noam's post is here:
http://www.pairlist.net/pipermail/retros/2007-June/002059.html

How common or rare is this? To find out, I used my chess engine (which
implements A1.3) to analyze 2.3M games from the ICOfY game database. The
results:

- 0.023% of games have at least one illegal move

- 0.00036% of plies are illegal

- I found 19 more examples of illegal moves played by 2700+ rated
players since 1998, including one by the current world champion,
Viswanathan Anand. Most examples are due to insufficient material (like
in the Mamedyarov-Anand game), but I found one example of "forced
insufficient material"

Loek Van Wely (2625) vs Leinier Dominguez (2717), Wijk aan Zee, 2009
http://www.chessgames.com/perl/chessgame?gid=1531105

and two examples of "forced stalemate", such as
Alexander Grischuk (2720) vs Boris Avrukh (2652), Saint Vincent, 2005
http://www.chessgames.com/perl/chessgame?gid=1363625

- there is a game with a sequence of 18 illegal plies
Mikhail Glukhov (2205) vs Ilia Shkurikhin (2417), Tomsk, 2009

There are more details on my website at
http://wismuth.com/chess/illegal-moves.html

	Francois