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+This file contains a description of GNU's heuristics.
+   Copyright (C) 1986, 1987 Free Software Foundation, Inc.
+
+This file is part of CHESS.
+
+CHESS is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY.  No author or distributor
+accepts responsibility to anyone for the consequences of using it
+or for whether it serves any particular purpose or works at all,
+unless he says so in writing.  Refer to the CHESS General Public
+License for full details.
+
+Everyone is granted permission to copy, modify and redistribute
+CHESS, but only under the conditions described in the
+CHESS General Public License.   A copy of this license is
+supposed to have been given to you along with CHESS so you
+can know your rights and responsibilities.  It should be in a
+file named COPYING.  Among other things, the copyright notice
+and this notice must be preserved on all copies.  */
+
+ -- requested by main author
+Heuristic descriptions for CHESS.
+
+Revision: 12-16-87
+
+Copyright (c) 1987 by John Stanback
+
+  Here is a brief description of the heuristics used in the positional 
+  evaluator of the GNU Chess program. Many heuristics are functions of the 
+  stage of the game which is based on the total non-pawn material remaining 
+  for both sides. 
+    
+
+PAWNS
+    The material value of a pawn is 100 points. Isolated pawns get a 
+    penalty depending on which file they occupy: 
+       (12,14,16,20,20,16,14,12) for files (a..h).
+    Doubled pawns (which are not also isolated) get a penalty of 12 
+    points. Backward pawns (defined simply as not being defended by a 
+    pawn with the square in front also not defended by a a pawn) are 
+    penalized 6 points. A 4 point penalty is also invoked for each attack 
+    by the opponent to a backward pawn and for a backward pawn on a 
+    half-open file. Pawn Advancement in the centre is given a bonus of 
+    about 4 points per rank in the opening increasing to about 8 points 
+    per rank in the ending. Advancement on the edges is given a lower 
+    bonus. Pawns on the e and d files and on the 2nd rank are given a 10 
+    point penalty. An additional penalty of 15 points is invoked if these 
+    pawns are also blocked. Pawns within 2 squares of the king are given 
+    a 10 point bonus. Passed pawns are given a bonus for increasing rank 
+    which is a function of stage of the game and of whether the opponent 
+    blocks or attacks one or more squares in front of the pawn or if the 
+    opponents king is in the square of the pawn. This bonus ranges from 
+    about 15 points for a pawn on the second rank up to about 300 points 
+    for a passed pawn on the 7th rank which can't be stopped from 
+    queening. 
+              
+
+KNIGHTS
+    The material value of a knight is 330 points. The main heuristic for 
+    knights is a bonus for proximity to the centre. This varies from 0 
+    points in the corners to 30 points in the centre. Knights are also 
+    given a bonus for being within 2 squares of each enemy piece. This 
+    bonus is a function of the stage of the game, equalling 4 points in 
+    the end game. A penalty of 1 point per square is given for distance 
+    from either king. A bonus of up to 8 points (depends on stage) is 
+    given for knights which can't be driven away by enemy pawns. 
+
+
+BISHOPS
+    The material value of a bishop is 330 points. Bishops are given a 
+    bonus as material falls off the board equalling 10 points in the end 
+    game. Bishops get a bonus for mobility and Xray mobility thru pieces 
+    but not pawns. This bonus ranges from -4 points for a totally blocked 
+    bishop up to 18 points for a bishop attacking 12 or more squares. 
+    Xray attacks on an enemy R,Q,K or any undefended piece are given an 8 
+    point bonus. Bishops are given a bonus of 14 points if they lie on 
+    the edge of the board up to 22 points if the lie in the centre. A 
+    bishop is given a bonus of up to 5 points for each attack to a square 
+    adjacent to the enemy king. 
+
+
+ROOKS
+    The material value of a rook is 520 points. Rook mobility is handled 
+    similiarly to bishops with a bonus of 0 points if blocked up to 20 
+    points if attacking 12 squares or more. A bonus of 8 points for Xray 
+    attacks is handled as it is for bishops. Rooks are given a bonus of 
+    10 points for occupying a file with no friendly pawns and a bonus of 
+    4 points if no enemy pawns lie on that file. After the opening Rooks 
+    are penalized slightly depending on "taxicab" distance to the enemy 
+    king. 
+  
+
+QUEENS
+    The material value of a queen is 980 points. The only heuristic for a 
+    queen is that after the opening it is penalized slightly for 
+    "taxicab" distance to the enemy king. 
+
+
+KINGS
+    Kings are given a penalty for proximity to the centre in the opening 
+    and a bonus for proximity to the centre in the endgame. The penalty 
+    is about 24 points for being in the centre in the opening with a 
+    bonus of about 36 points for being in the centre in the endgame. 
+    Kings are penalized for lying on an open or half-open file or if the 
+    adjacent file closest to the corner is open or half-open. This 
+    penalty is up to 23 points in the opening and goes to zero in the end 
+    game. The King is penalized up to 8 points if there are no pawns 
+    immediately adjacent. A penalty is invoked depending on the number of 
+    "safe" checks available by the opponent. This penalty ranges from 6 
+    points for one such check to 50 points for 4 or more. Depending on 
+    game stage, Kings are given up to 10 points for castling and a 
+    penalty of up to 40 points for moving before castling. 
+  
+
+SPECIAL
+    If more than one piece is "hung" (attacked and not defended or 
+    attacked by an enemy piece of lower value) an extra penalty of 10 
+    points is invoked for that side and the search may be extended one 
+    ply. Pinned or trapped pieces are treated similarly. A special mating 
+    routine is used if one side has only a king and the other has mating 
+    material. 
+