Computer Chess Club Archives




Subject: Symbolic: From bitboards to ideas

Author: Steven Edwards

Date: 08:52:07 03/13/04

Consider the position BWTC.0025:

[D] r1bq1r1k/ppp1N1p1/7p/2bp1pN1/2Bn1B1Q/8/PP3PP1/R3R1K1 w - - 0 1

It's a mate in three starting with 1. Qxh6+; however, I picked it for an example
as it also has a number of possible knight forks for White.

A traditional chess programs can discover knight forks only by search.   A goal
for Symbolic is to recognize tactical motifs via pattern matching, use these
ideas for plan formation, and then use the plan to guide a very narrow search to
produce a verification of the plan.

So, here's some sample test code to recognize, without search, potentially
interesting knight forks.  It's an example of bridging the gap between bitboards
and ideas.

(defun SKF (MyFEN)
    "Interactive tester for SuggestKnightForks"
    (let* ((PosVal (PosValFromFEN MyFEN)) (MoveVals (GenerateVal PosVal)))
        (SuggestKnightForks PosVal MoveVals)))

(defun SuggestKnightForks (MyPosVal MyMoveVals)
    "Return a list of potential knight fork ideas"
            (Ideas nil)
            (AColor (ActiveColorFromPosVal MyPosVal))
            (PColor (OtherColor AColor))
                    (BBLocByColorPV MyPosVal PColor)
                    (BBLocByManPV MyPosVal (ManFromColorPiece PColor Knight))))
                    (ManFromColorPiece AColor Knight)))
        (dolist (MoveVal MoveVals)
            (let ((Idea nil) (VictimManSqList nil))
                (setf VictimManSqList
                                (AttackByKnightBB (ToSqFromMoveVal MoveVal))
                (when (> (length VictimManSqList) 1)
                    (setf Idea
                            (list 'try MoveVal)
                            (list 'escape (first VictimManSqList))
                            (list 'capture (second VictimManSqList))))
                    (format t "Idea: %u %n" Idea)
                    (push Idea Ideas))))

Running the above with BWTC.0025 produces:

Idea: ((try Nxf5) (escape (BlackPawn h6)) (capture (BlackPawn g7)))
Idea: ((try Ng6+) (escape (BlackKing h8)) (capture (BlackRook f8)))
Idea: ((try Nf7+) (escape (BlackKing h8)) (capture (BlackQueen d8)))
Idea: ((try Ne6) (escape (BlackQueen d8)) (capture (BlackRook f8)))
Idea: ((try Nc6) (escape (BlackQueen d8)) (capture (BlackPawn a7)))

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Last modified: Thu, 15 Apr 21 08:11:13 -0700

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