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Subject: Re: EPD opcodes and mate scores

Author: Dann Corbit

Date: 12:06:09 12/17/01

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On December 17, 2001 at 14:53:12, Rafael Andrist wrote:

>In the PGN/EPD specification I couldn't find any human friendly way to indicate
>the distance to the mate if it is the side the move which will be mated. I know
>it would be possible with the "ce" opcode but this is a little bit more
>difficult to read. Is there any way to indicate it in an easy way like the "dm"
>it does if the side to move mates the opponent? Should I use e.g. "dm -3" or is
>this a bad idea? Any suggestions?

From the PGN Standard, we have this:
-------------------------------------------------------------------------------
16.2.5.7: Opcode "dm": direct mate fullmove count

The "dm" opcode is used to indicate the number of fullmoves until checkmate is
to be delivered by the active color for the indicated position.  It always
takes a single operand which is a positive integer giving the fullmove count.
For example, a position known to be a "mate in three" would have an operation
of "dm 3;" to indicate this.

This opcode is intended for use with problem sets composed of positions
requiring direct mate answers as solutions.
-------------------------------------------------------------------------------
Because of the statement "by the active color" I think negative numbers are out.

Unfortunately, *most* implementers of PGN ignore the correct use of the ce
opcode (though I think 32767 should be allowed for 'this is a checkmate' rather
than used for indication of error).  At any rate, you cannot count on 32767-n
being ply distance to mate.  All sorts of values are used, and that is why
distance to mate is unclear.  Because people ignore the standard.

My suggestion is:
c0 "Mate in three for the opposing side."



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