difficult endgame test

[bob]

I ran this with crafty... it finds this move at depth=11, .1 seconds, on my core2 duo laptop. by depth=18, .5 seconds, the score is in black's favor by 1/2 pawn.... by depth 21, it is 1.5 pawns in blacks favor, taking about 2 seconds...

Hamsters misses but it's all in the evaluation... I followed Crafty's PV up to the last pawn capture and king move:

[D]8/6p1/8/4p2k/3pP3/3P2K1/2P5/8 b - - 1 1

and here Crafty sees an advantage for black while Hamsters thinks this is even slightly better for white!

How do you score the passed pawn g7 in this case?

It is winning. black advances the pawn and white has to take the time to capture it. Black abandons it at the right point and penetrates to eat the white pawn chain.

The method you describe is usually how to win with a passed pawn, and would of course also work here. However in this case an even faster and easier winning method is to advance the g pawn, supported by your king, until White's king would be stalemated (if he didn't have a pawn move). Then White is forced to advance his pawn, Black captures it and advances this second pawn to promote on c1 with mate.

That won't quite work as described. If white is stalemated except for the pawn push, he pushes the pawn and now black can't take it or this is a repeat where now white has to push the other pawn, and if that one is taken, the game is drawn...

but here, g5 wins as easily as the king move, just to me the king move follows a known strategy for winning these, where if you remove the other pawns, g5 would turn this into an instant draw.

It works exactly as I described. After Black captures the first pawn (c-pawn) now White can push the d-pawn so it is still not stalemate. Black does not capture after White pushes the d-pawn ... he just runs the c-pawn down for mate.

Correct of course. Was not thinking about the now movable white pawn...

[bob]

an outside passer is far safer to reward than things like a rook on the 7th, yet everyone does the latter, but not the former. outside passed pawns are a very common theme in endings. distant majorities are more difficult, but also need to be recognized for the very same reason. It is stupid to find a way to win a pawn but leave your opponent with a distant passer or distant candidate passer, which loses the game once the program searches deep enough to realize what it has done.

Are you talking about players or programs?

Somtimes you need a rook on the seventh to get the latter, or a quick mate!

I'm talking about both. A rook on the 7th doesn't survive there very long. It can be a "fleeting advantage". A distant passed pawn is more durable and becomes more important as the game progresses. That was my point.

Many current "positional scores" in chess programs are incorrect because you give up A to get B, but you can't keep B, yet A is gone so you end up down whatever A was. Distant passers are less likely to disappear and are also potentially more decisive...

So if one rewards rooks on open files and rooks on the 7th rank, among other things. Rewarding distant passers is even less of a risk than rewarding the rook(s).

[Terry McCracken]

an outside passer is far safer to reward than things like a rook on the 7th, yet everyone does the latter, but not the former. outside passed pawns are a very common theme in endings. distant majorities are more difficult, but also need to be recognized for the very same reason. It is stupid to find a way to win a pawn but leave your opponent with a distant passer or distant candidate passer, which loses the game once the program searches deep enough to realize what it has done.

Are you talking about players or programs?

Somtimes you need a rook on the seventh to get the latter, or a quick mate!

I'm talking about both. A rook on the 7th doesn't survive there very long. It can be a "fleeting advantage". A distant passed pawn is more durable and becomes more important as the game progresses. That was my point.

Many current "positional scores" in chess programs are incorrect because you give up A to get B, but you can't keep B, yet A is gone so you end up down whatever A was. Distant passers are less likely to disappear and are also potentially more decisive...

So if one rewards rooks on open files and rooks on the 7th rank, among other things. Rewarding distant passers is even less of a risk than rewarding the rook(s).

Yes as a general rule I agree. There are times the Rook will just win, but not always, and I too put more weight on the outside passed pawn.

There are exceptions of course, it depends on the position, but as a rule the outside passed pawn is permanent and winning, at least if all the pieces are off the board

Reduce and Simplify Regards,
Terry