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Strelka (Стрелка, Russian for "little arrow"),
a chess program by Jury Osipov which appeared as closed source engine in May 2007. Its successor, Strelka 2.0 was released as open source program in January 2008. Strelka 2.x became runner up behind WildCat at the 1st Computer Chess Championship of CIS Countries in 2008.

From the very beginning Strelka was suspected not to be original but derivative work as elaborated below. What kind of syllogism from the claims and statements by Vasik Rajlich, Fabien Letouzey, Jury Osipov and others applies, remains to be seen. However, it is more likely the ethical issues of computer chess programming are affected rather than the legal ones.
Strelka on tour [1]

Clone Suspicions

Almost immediately after Strelka's initial release, there were suspicions due to various similarities found in solving certain test-positions [2] [3], that Strelka might be a clone of Rybka 1.0 Beta. The attempt by Sergei Markoff after reviewing its sources to declare Strelka original, seemed rather pointless due to the closed sources of the now commercial Rybka [4], but it was also confirmed by Bryan Hofmann [5][6], who according to Markoff is a compiler expert who also did Rybka compiles and was aware of its sources [7] . Additionally, an "expert's opinion" was called from Dann Corbit to declare Strelka "clean" [8][9]. Fabien Letouzey, who was consulted by Dann, put a short note that Strelka 1.x source was not a verbatim copy of his open source engine Fruit, but revealed more details on that issue years later in January 2011, when he was long out of computer chess business and coincidentally got aware of the Strelka affair [10] [11] .

In the meantime, in July 2007, Jury Osipov admitted Strelka was based on Fruit rewritten to bitboards, and was successively improved in evaluation and search with correlation analysis of Rybka's assessment of the positions. Osipov further mentioned he studied Rybka using a disassembler, to achieve an even greater similarity, and that he felt that Vasik Rajlich likely walked the same path as he did, essentially to rewrite Fruit to bitboards and include material imbalance tables by Larry Kaufman [12].

Strelka 2.0

In January 2008, the new Strelka version 2.0 released was open source, and everybody could compare Strelka 2.0 with the Fruit sources for the similarities or not, and whether the claims of Jury Osipov were correct. Notably, a few days later, Vasik Rajlich declared Strelka 2.0 a Rybka 1.0 Beta clone [13] , which on the other hand raised further suspicions on the origins of Rybka.

Strelka 5

In October 2011, Strelka 5 was released as closed source engine, according to Jury Osipov incorporating ideas of Rybka 3, Ippolit, Houdini, Critter and Stockfish, as well as own innovations [14] [15].

See also

Forum Posts




2012 ...

External Links

Chess Engine



  1. ^ Soviet space dogs from Wikipedia - Belka and Strelka
  2. ^ Re: My Tests with Strelka by Eduard Nemeth, CCC, May 07, 2007
  3. ^ Re: TO BE OR NOT TO BE by Mike Scheidl, CCC, May 07, 2007
  4. ^ Sergei Markow about Strelka by Werner Schüle, CCC, May 09, 2007
  5. ^ My review of Strelka Code by Bryan Hofmann, CCC, May 12, 2007
  6. ^ Strelka 1.8 source code review by Bryan Hofmann, CCC, October 01, 2007
  7. ^ To put everything into place with Strelka by Sergei Markoff, CCC, May 10, 2007
  8. ^ Re: My review of Strelka Code by Dann Corbit, CCC, May 12, 2007
  9. ^ Re: Is strelka a clone? by Dann Corbit, CCC, July 09, 2007
  10. ^ Fabien's open letter to the community by Tord Romstad, CCC, January 23, 2011
  11. ^ Fabien's open letter to the community by Tord Romstad, Open Chess Forum, January 23, 2011
  12. ^ new translation of J.Osipov statement in KasparovChess forum by Evgenii Manev, CCC, July 12, 2007
  13. ^ Strelka 2.0 by Vasik Rajlich, Rybka Forum, January 11, 2008
  14. ^ Народ.Ру: Осипов Юрий (Russian)
  15. ^ Strelka 5 by Yuriy Osipov by Slavik Pavloff, CCC, October 15, 2011
  16. ^ Anthony Cozzie speaks about Rybka source code from Steve Lim / SuperSteve3d - Home, February 04, 2008
  17. ^ Anthony Cozzie speak ! by Silvian, Rybka Forum, February 03, 2008

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