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Conference rusure::math

Title:Mathematics at DEC
Moderator:RUSURE::EDP
Created:Mon Feb 03 1986
Last Modified:Fri Jun 06 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:2083
Total number of notes:14613

1737.0. "Chess Problem" by HERON::BUCHANAN (The was not found.) Mon Mar 29 1993 14:09

+--+--+--+--+--+--+--+--+
|  |  |  |  |  |  |  |  |
+--+--+--+--+--+--+--+--+
|BK|  |  |  |  |  |  |  |
+--+--+--+--+--+--+--+--+
|  |  |  |BP|  |  |  |  |
+--+--+--+--+--+--+--+--+
|BP|  |  |WP|  |BP|  |  |
+--+--+--+--+--+--+--+--+
|WP|  |  |WP|  |WP|  |  |
+--+--+--+--+--+--+--+--+
|  |  |  |  |  |  |  |  |
+--+--+--+--+--+--+--+--+
|  |  |  |  |  |  |  |  |
+--+--+--+--+--+--+--+--+
|WK|  |  |  |  |  |  |  |
+--+--+--+--+--+--+--+--+

	Here's a pretty piece of Internet flotsam.   White to play and win, or
Black to play and draw.   What is interesting is the *mechanism* of proving the
result.

Andrew.
T.RTitleUserPersonal
Name
DateLines
1737.1the Black drawHERON::BUCHANANThe was not found.Wed Mar 31 1993 11:1129
	The easier half of the problem.   Forget about the precise position
of the kings at the moment, and label some of the squares on the board.

+--+--+--+--+--+--+--+--+
|  | i| j| k| l| m| n|  |
+--+--+--+--+--+--+--+--+
|  | b| c| d| e| f| g|  |
+--+--+--+--+--+--+--+--+
|  | a|  |BP|  |  | h|  |
+--+--+--+--+--+--+--+--+
|BP|  |  |WP|  |BP|  |  |
+--+--+--+--+--+--+--+--+
|WP|  | a|WP|  |WP|  | h|
+--+--+--+--+--+--+--+--+
| b| c| b| c| d| e| f| g|
+--+--+--+--+--+--+--+--+
| i| j| i| j| k| l| m| n|
+--+--+--+--+--+--+--+--+
| b| c| b| c| d| e| f| g|
+--+--+--+--+--+--+--+--+

Whenever the White king moves, the Black king should move to the square of the
same label.   Since the mapping from the White king's orbit to the Black's
preserves adjacency, the Black king can alway do this.   Whenever the White
king is at a or h, the Black king prevents him from penetrating Black lines.

So to start this up, the Black king must move to b7, and draws.

Andrew
1737.2CSC32::D_DERAMODan D'Eramo, Customer Support CenterWed Mar 31 1993 11:4926
        Your labels are different than the ones I used. :-)  After
        noting the key points b5 and h5 and the corresponding squares,
        the win I had come up with White to move looked like
        
        	1. Kb1, Ka8 or Ka6 2. Kb2, Ka7 3. Kb3, resigns :-)
        
        and at the end, or if black varies earlier, the correspondence
        is broken (and so White can force through to either b5 or h5).
        
        For example, if White moves to d3 (labelled c) when Black is
        already at c7 (also labelled c), then Black must either fall
        back out of reach of b6 (then White moves to c4 and next b5)
        or move to the b file (then White races to h5).

        Examples if Black varies early are 1. Kb1, Kb6. 2. Kc2 and
        if Black moves to a square with a 'b' or 'c' label then White
        does the same.  If Black retreats to the a file then White
        reaches h5.  But those are all of Black's choices.  For example,
        2. ..., Kb7 3. Kb3 and if Black drops to the 8th rank or goes
        to b6 then White plays to c4 and b5 next move; otherwise Black
        moves to c7 and White to d3 (see previous paragraph).
        
        How to win after White plays to h5 with Black on the f file
        is left to the reader. :-)
        
        Dan