# [Retros] Illegal moves by grandmasters

Francois Labelle flab at wismuth.com
Wed May 11 02:29:50 EDT 2011

I agree that my title is provocative, but I think that the logic behind
it is sound, so why not? :)

Yefim Treger wrote:

> IMO: an illegal move is a move, which breaks fundamental rules of

> chess (piece movement, etc.)

So according to you, some rules are "fundamental" and others are not,
and breaking a fundamental rule would be illegal, but breaking a
non-fundamental rule would be called something else (called what?). The
FIDE rules make no such distinction.

> Mathematically: Imagine the tree of all positions (including dead

> ones, etc.). Each position is a vertex, edges between them are the

> legal moves. The Illegal moves do not correspond to any edges.

Rephrasing the rules of chess as a graph doesn't change anything.
Actually I like it because it forces a black-and-white interpretation of
the rules. In that graph, Article 5.2b says that dead positions have no
outgoing edges, so playing a move from a dead position does not
correspond to an edge and so according to your logic it is illegal.

Noam Elkies wrote:

> This kind of "illegality" is a fun addition to the arsenal of a

> problemist, but doesn't change the outcome of over-the-board games,

> as long as "dead" draws are still not affected by the clock.

It's true that A1.3/A5.2b/A9.6 don't change the outcome (win/draw/loss)
of over-the-board games much, but that's irrelevant. The rules are there
so Mamedyarov's 69.Kd4 is illegal. If FIDE had wanted 69.Kd4 to be
legal, then those rules would not be there or they would have been
written differently.

Guus Rol wrote:

> The reverse however is not true. The (composed) dead positions

> published by Andrew Buchanan are indeed illegal as no legal game

> can be construed to arrive at them. The "law" does not allways look

> the same in forward and backward direction.

I don't follow your logic. Andrew's chess page shows a problem with 2
kings and the caption "Who moved last?". The answer is supposed to be
White, but here's a game

Hermansson Emil (2432) vs Nilssen John Arni (2372), Tvoroyri, 2005
http://chess-results.com/partieSuche.aspx?art=36&tnr=2381&rd=9&weiss=5&lan=7

which shows that it's possible for Black to have moved last. So either
that game is illegal or Andrew's problem is flawed. I don't see how you
can have it both ways.

Francois