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MatPlus.Net Forum General Helpmate Material
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(1) Posted by Hauke Reddmann [Wednesday, Aug 26, 2020 11:01]

Helpmate Material

Since it is relevant for FIDE "Insufficent Material for Mate",
is the following correct?

Assuming that a) there is no forced forward play and b) the
position is "open", then the *only* insufficient material is
K vs any, KBB... vs KBB... (any number) with all bishop(s) on same color,
KBB...(same color) vs K+any number of heavies, and KS vs KQQQ...
Everything else allows some h#.
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(2) Posted by Marcos Roland [Wednesday, Aug 26, 2020 12:58]

"Open position" implies that any pawn can be promoted?
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(3) Posted by Jakob Leck [Wednesday, Aug 26, 2020 16:28]

In principle you could add the dead positions K vs K and KS vs K to your list.
But I think you are referring to the case where a player would lose on time unless "the position is such that the opponent cannot checkmate the player’s king by any possible series of legal moves" (Fide laws 6.9), in which case the dead position should already have ended the game before.
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(4) Posted by Siegfried Hornecker [Wednesday, Aug 26, 2020 16:28]

"open position" means there are no closed clusters like in the bottom right corner here:
(= 9+4 )

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(5) Posted by Andrew Buchanan [Wednesday, Aug 26, 2020 16:39]

Hi Hauke,

As Jacob surmises, you must be referring to the lesser-known *one-sided* death in FIDE Laws Article 6 The Chessclock.

Article 6.9 Except where one of Articles 5.1.1, 5.1.2, 5.2.1, 5.2.2, 5.2.3 applies [mate, resignation, stalemate, dead position, agreed draw], if a player does not complete the prescribed number of moves in the allotted time, the game is lost by that player. However, the game is drawn if the position is such that the opponent cannot mate the player’s king by any possible series of legal moves.

In open position, the opponent must still not be able to mate even if he eliminates *all* of the player's pieces. So opponent has K, KN or KB^n (where all bishops are on the same colour squares). Now what can we give the player, so he is still safe? K v KX^m, or KN v KQ^m, or KB^n v KH^m, where X is anything, & H is B (still of that same colour), R or Q.

It's nevertheless possible to place a mate position on the board with some of this material, although it's not reachable in a legal game:

(= 3+3 )
It can moreover be reached by a legal move. If White is to move in:

(= 3+3 )
then they can play 1.Be7#. Of course this starting position with White to move is illegal because it's not reachable itself by a sequence of legal moves, since White is already checking Black. However that's a problem only with the history of the game: there's nothing stopping White continuing to play.

Article 5.5.1 The game is won by the player who has checkmated his opponent’s king. This immediately ends the game, provided that the move producing the checkmate position was in accordance with Article 3 and Articles 4.2 – 4.7.

Note in particular 3.10 defining and distinguishing legal move, illegal move & illegal position (but not, curiously, legal position). 5.5.1 asks only that the move producing the checkmate position be legal according to Article 3. The prior position clearly is illegal, but this is irrelevant under 5.5.1. So the impossible mate above is "achievable" in some silly sense.
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(6) Posted by Hauke Reddmann [Wednesday, Aug 26, 2020 19:24]

OK, lessee how I deal with that and my fresh new national arbiter license :-)

So, we assume it's a blitz game, Black just played Rc8 which is his first
illegal move, then his flag fells. He then claims insufficient material.
Since the flag fell, the game is over anyway and the illegal move won't be
corrected. (The arbiter had his eyes elsewhere and did not interfere on A4.2,
and White doesn't intend to claim, so Rc8 stands.) White could play
Be7# indeed and thus claim a win...oh, the FIDE just amended their rules
with §14, "All Problemists should be shot! NOW!" :-)
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MatPlus.Net Forum General Helpmate Material