readme for "40H-EPD-databases".

"40H-EPD-databases" is copyright (c) 2014-23 by Norman Pollock. 
All rights reserved.

These databases are freeware. They contain chess positions 
available in the Public Domain on the Internet or elsewhere, and 
were edited by Norman Pollock.

No warranty, expressed or implied, is made that the information 
provided in "readme-epd-db.txt" or in the positions, is accurate. 

No warranty, expressed or implied, is made as to the worthiness 
of these files for computer or chess usage. 

The user bears full responsibility for any consequences from 
the use or misuse of these files. The editor is not responsible 
for any damages or losses of any kind.

These databases can be freely distributed provided they are 
distributed "as is". The editor is not responsible for any 
changes made by others.

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Overview:

"40H-EPD-databases" contain checkmate puzzles from 2 to 7 moves. 

They are organized into 12 files:

mate-b2.epd, mate-b3.epd, mate-b4.epd, mate-b5.epd. mate-b6.epd, 
mate-b7.epd
  
mate-w2.epd, mate-w3.epd, mate-w4.epd, mate-w5.epd. mate-w6.epd, 
mate-w7.epd
 
The "mate-bX.epd" and "mate-wX.epd" files contain checkmate puzzles
with a forced mate in "X" moves and where "b" or "w" represent the
color to move. For example, "mate-b3.epd" contains forced mate 
puzzles in "3" moves for "Black".

There are 4 extra files:
mate-all.epd, mate-all-w.epd, mate-all-b, mate-all.pgn (which uses
FEN tags).

A "pgn" viewer is recommended.

There are no duplicate positions in the collection. 

There are no false "en passant" target squares.

Each solution has a unique FIRST move. Thereafter, there could be
multiple paths to a forced mate in the indicated number of moves.

Games with multiple FIRST moves to checkmate removed.

Each puzzle has a "flipped" version with colors reversed. Such 
pairs have the same "ID".

"40H-EPD-databases" has 2 download sites:

  40hchess.epizy.com

  nk-qy.info/40h  (Thanks to Frank Quisinsky)

Please bookmark.
 
contact: rc1242(at)yahoo(dot)com

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More details:

Each "epd" record (puzzle) has a "bm" opcode ("best move"),
a "ce" opcode ("centipawn evaluation" which has been converted
to "distance to mate") and a "pv" opcode ("predicted variation"). 
All the "epd" records in this collection have only ONE "best move" 
(first move) that leads to a forced checkmate in the specified 
minimum number of moves. There may be other variations that lead 
to a checkmate in the same specified minimum number of moves, but 
they all start with the same first move.

The "ce" opcode is evaluated from the viewpoint of White, as 
required by "PGN Standards". This opcode indicates the numerical
evaluation of the position in centipawn units, which has been 
converted to the minimum distance to a forced mate. A path to mate 
for White will have a positive value such as "+M3", and a path to 
mate for Black will have a negative value such as "-M3".

The "id" opcode shows the "id" number supplied by the editor. Each 
record has a flipped version with the same "id" number. A flipped 
version has the colors reversed and the pieces flipped in a vertical 
reflection over the imaginary horizontal line between ranks "4" and 
"5". The color to move, "castling" rights. and "en passant" rights 
are also reversed. The new "epd" record is logically equivalent to 
the old "epd" record.

To get a visual comparison, open 2 instances of your "PGN viewer". 
Put the original "epd" record in one instance, and put the "flipped" 
"epd" record in the other. Be sure both "PGN Viewers" have the same 
"View". For example, neither is in "flip" view mode. Compare.

  1k6/1Pr5/K1nR1p2/4p3/4P3/4BP2/8/8 w - - bm Rd6-d8+; ce +M2; pv Rd6-d8+ Rc7-c8 b7xc8Q+; id "104";

  8/8/4bp2/4p3/4P3/k1Nr1P2/1pR5/1K6 b - - bm Rd3-d1+; ce -M2; pv Rd3-d1+ Rc2-c1 b2xc1Q+; id "104";

Users should be acquainted with classical checkmating patterns: 

  https://en.wikipedia.org/wiki/Checkmate_pattern
  
Positions are from the Public Domain and then edited. 

Filter: Material of the attacking side (side to move) does not 
exceed opponent's material by more than 3 pawn units where P=1, 
N=3, B=3, R=5, and Q=9 pawn units.

These files were constructed using "ChestUCI v5.2" by Franz Huber 
(based on "CHEST v3.19" by Heiner Marxen), "Arena 3.5.1" by Martin 
Blume, "40H-EPD" tools by Norman Pollock, and "PGN-Extract" by 
David Barnes.

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