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Re: GNU Backgammon Clones

From: Øystein Schønning-Johansen
Subject: Re: GNU Backgammon Clones
Date: Wed, 23 Jun 2021 11:31:54 +0200


Good points, Ian. Maybe it is possible to "reverse engineer" the executable code of the potential clones and see if it matches the weights of a neural network from GNU Backgammon. The weights of a neural network will indeed be sequential in memory as in GNU Backgammon. This will be strong enough prof to bust someone. THat is a much stronger prof than vaguely claiming they play the same moves. However, these take competence of decomiling and investigation of windows executables. (A competence I do not have, but may be able to learn)

What do we intend to do if we can confirm that these are real clones? I guess the "author" doesn't make a lot of dough from his sales?


On Wed, Jun 23, 2021 at 10:46 AM Ian Shaw <Ian.Shaw@riverauto.co.uk> wrote:

Hi Jeurgen,


The techniques for creating a strong backgammon program are well known, and any strong bot is going to make the same move as another strong bot, simply because it is the correct move.


The main way to demonstrate that the nets are identical is to show that they make the same move in all circumstances. This is complicated by the fact that the net can be set with various evaluation parameters so that the same network will make different moves, depending on the search depth, move-pruning settings and so on.


I’m afraid I can’t help with getting hold of old versions. Perhaps some of the developers would know if they are somewhere in the depository.


What is the problem you are trying to solve? Gnubg is an open source program, so people are allowed to take it and use it as they like, even to the point to selling it. However, they would be breaching the licence if they didn’t include the gnu licence in their software and make the source code available. Is this your concern.



n  Ian Shaw


From: Bug-gnubg [mailto:bug-gnubg-bounces+ian.shaw=riverauto.co.uk@gnu.org] On Behalf Of Juergen Schaefer
Sent: 22 June 2021 22:35
To: bug-gnubg@gnu.org
Subject: GNU Backgammon Clones


Hi !


GNU Backgammon Clones


It's a very "sensitive theme" and a difficult problem: cloning.

Is it possible to track down, to prove that a certain program is a clone of GNU Backgammon ?


Since about 20 years there are some programs commercially available (by the same author)...

frankly spoken I believe that all these programs are not driven by an original engine,
but their evaluation engines are based on GNU Backgammon.
IMHO in fact it's GNUBG in disguise, simply put: clones.


We have only the source code of one program (GNUBG) - a direct comparison isn't possible.

So I can only try to collect circumstantial evidence instead.


GNUBG started in 1999, shortly afterwards (about 2001) the first suspected program

was on the market.
Until now there are at least 6 of them published by the same author.


The features of the "clones" are very similar to GNUBG's - the playing strength also.

Whereas the GUI of the "clones" is "shaky", almost clumsy.


For example there is a serious bug in the move generator, a "clone" doesn't accept

a possible move while bearing off !!


"Clone"      Opponent     pip count 87:27
Bar 1x       1   3x
9   1x       2   2x
18  2x       3   2x
20  3x       4   2x
22  3x       6   1x
23  3x       ab  5x
24  2x

Opponent rolls 5+3 - the (best) legal move 6/3 4/off isn't shown respectively
won`t be accepted at all by the "clone" GUI, the "clone program" accepts only
6/1 3/off and 6/1 4/1 !!


Really bad for a program that plays at world class level ! 


GNUBG has 5 main levels:
1. World class
2. Expert
3. Advanced
4. Intermediate
5. Beginner


Might happen by accident that the "clone programs" also always have 5 levels.


But how about the "treacherous" beaver feature:
beavers are not part of the official backgammon rules - so why bother with
this superfluous stuff ?


How many programs do you know which have implemented the option beaver 
being open source - exactly one, GNUBG - who else ?


The "clones" use another dice generator which appearantly isn't working very well:
2 identical games within a few hours with 8 moves respectively 36 moves each.
How likely is that ?


The identical games were played the same day within a few hours...the dice
generator of the "clones" seems to work quite odd...doesn't it ?

Repeating dice numbers within such a short period - Mersenne Twister provides
better randomness.


I think all "clone programs" are neural nets like GNUBG - not only like GNUBG,

Although at first sight it might look like that these programs have no bearoff database

nor weight files. Probably incorporated directly into the exe-files which are quite large

(about 4 MB) ?!


I am convinced that none of the "clone programs" will be better than GNUBG
of that corrrespondent time, perhaps a few elo points less.


Just another question about the similarity of GNUBG and the "clone programs":
not in the shareware versions, but in the full versions of the "clones"
there is a possibility to play over network, TCP/IP port.

How about GNUBG (around 2000) ?


The simple move generator bug in the GUI, which doesn't allow a legal move,
the lousy random generator and the missing possibilities of entering positions
and manual dice - this doesn't really fit together to the world class engine.
IMHO clear indications for cloning.


Additionally the autor has cloned his "own" program and sold under another label
exactly the same...- the versions from 2003 and 2005 are absolutely identical,
even the readme-file ! Ok...name and package were new...!!


Never heard of the author of the "clones" before - out of the box with world
class performance, absolutely brillant...not bad for a newcomer program -
but is it really a program written from scratch ?


I doubt - but it is still only an initial suspicion, possibly well founded,
but still no clear evidence. Definitely no final judgement.


At the moment I am collecting blunders of the "clone programs" then I would
like to do a "cross blundercheck" with GNUBG versions around the year 2000 .


Do you know if it is still possible to download very old versions of GNUBG
v. < 0.10, 1999-2000 ?


Seems to be the only chance to prove vast similarity...that will be tough,
as the "clones" do not provide the possibility to enter positions,
also manual dice entry is missing in all "clone programs".


These two elementary features never implemented in the last 20 years...why ?
Of course it's more difficult to reproduce, to compare games...


These "clone programs" definitely need further investigation..


Do you have any idea what can be done in order to prove or to refute my suspicion ?


All these points above leave a bad gut feeling to me. Am I on the right track ?
Or is my clone suspicion just clueless ?

For me it isn`t easy to verify if it's a clone or not - might be the experts can ?!


Any hint, any help much appreciated !

Thank you very much !


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