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Subject: Crafty and Repetitions

Author: Artem Pyatakov

Date: 22:37:56 07/17/01


I am not sure if Dr. Hyatt is back yet, so if someone else can answer this I
would appreciate it.

I was looking at the way Crafty handles repetition and came across the following
comment:
/*
 ----------------------------------------------------------
|                                                          |
|   insert the board into the next slot in the repetition  |
|   list.  then scan the list.  we look for the case where |
|   the position has been seen one time before, unless we  |
|   are at ply 1 or 2, where we must have seen the same    |
|   position twice prior to this.                          |
|                                                          |
 ----------------------------------------------------------
*/

There is also a related comment:
"note that for a repetition to happen in the first two plies of the tree, the
position has to be repeated three times, while for plies beyond two, two
repetitions trigger a draw score."

My question is this: Why does Crafty make this exception for plies 1 and 2? What
is special about them?

Thank you.

Artem Pyatakov



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