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a chess program by primary developer Chrilly Donninger, subsequently supported by members of the First Vienna Computer Chess Club (Nimzo Werkstatt) concerning testing, chess knowledge, opening book and hardware. The program was first dubbed Nimzo-Guernica in remembrance to Aron Nimzowitsch and as manifest of Chrilly's Anti-war engagement [1]. It had its tournament debut at the 3rd Computer Olympiad 1991 and further played the DOCCC 1991 and IPCCC 1991. At the WMCCC 1993, Nimzo-Guernica aka Nimzo-2 upset Mephisto Gideon [2] and later winner Hiarcs to lead the pack after five rounds, and finished strong fourth despite 1.5 points out of the last four rounds.
Aron Nimzowitsch [3]


David Bronstein playing Nimzo by Chrilly Donninger, Johan de Koning kibitzing, Aegon 1997 [4]


Guernica and Nimzo-2 were leaf evaluators to spent 60 to 70 percent of its time in evaluation. The main design criterion for Nimzo-3 was combining the positional play of Nimzo-2 with the tactical strength of a program like Fritz. Nimzo-3 therefor became a Genius/Fritz like program with a complex root evaluation [5], called Oracle as proposed by Hans Berliner [6] [7], and which seems to have been first used by Kaare Danielsen. The oracle approach with very simple, mainly first-order evaluation terms at the leaves, made Nimzo-3 to spent about only 10 to 20 percent on leaf evaluation, yielding in an increased node rate of 400%.


The CHE and CHE++ declarative language for expressing chess knowledge using a GUI was used to incorporate planning features within the oracle used [8].


During the WMCCC 1996, Nimzo was still amateur, but soon went commercial as MS-DOS program Nimzo 3.5 and the Windows program Nimzo 2000 distributed by Weiner's Millennium 2000 GmbH, later released as Chess Engine Communication Protocol compliant engine WBNimzo. Nimzo98, Nimzo99 were native ChessBase engines, followed by Nimzo 7.32 and Nimzo 8 and its derivation Schweinehund [9] [10].


given in 1999 from the ICGA tournament site [11]:
Nimzo is one of the leading professional chess programs. It combines sound positional play with extremely strong tactics. Nimzo-Paderborn is a considerable improved version of the currently commercially available programs Nimzo98, Nimzo99 and Nimzo2000.

Nimzo-Paderborn learns automatically from human grandmaster games. It is also equipped with an own Chess-Advice-Language (Che++) which allows strong human players to formulate chess-knowledge. The program can also access in its search endgame databases. It therefore searches regularly from the middlegame into won endgames.

Forward Pruning in Nimzo 2.2.1

Following forward pruning code appears in Nimzo's 2.2.1 search routine [12] applied at frontier nodes, notably the aggressive Lang mode at pre-pre-frontier nodes or below. The source was published along with a foreword by Donninger in 2002 [13] :
  if((depth <= 1) && (!extflg) && (score > beta) && (GPtr->hung.w <= KNIGHTHUNG)) {
    return score;
  if(LangModus) {
    if((depth <= 3) && (!extflg) && (score > beta) && (GPtr->hung.w == 0)) {
      return score;

See also


Forum Posts

External Links


  1. ^ Bombing of Guernica from Wikiepedia
  2. ^ With the help of a sign bug in passed pawn evaluation, see Chrilly Donninger (1999). Computer machen keine Fehler. CSS 2/99, pdf (German)
  3. ^ Aron Nimzowitsch from Wikipedia
  4. ^ David Bronstein vs. Nimzo, Photo by Thorsten Czub from Aegon 1996-97
  5. ^ Chrilly Donninger (1996). CHE: A Graphical Language for Expressing Chess Knowledge. ICCA Journal, Vol. 19, No. 4
  6. ^ Hans Berliner (1987). Some Innovations Introduced by Hitech. ICCA Journal, Vol. 10, No. 3
  7. ^ Hans Berliner (1989). Some Innovations Introduced by Hitech. Advances in Computer Chess 5
  8. ^ CHE docs in English / Nimzo 3 version by Mike S., CCC, November 22, 2001
  9. ^ Re: Versions of Nimzo by Shep, CCC, December 12, 2000
  10. ^ Re: Nimzo 4 by Manfred Meiler, CCC, November 19, 2002
  11. ^ Nimzo's ICGA Tournaments
  12. ^ Nimzo: sr.c: search-tree handling hosted by Roger Thormann
  13. ^ Vorwort von Chrilly Donninger (German) hosted by Roger Thormann
  14. ^ Braille from Wikipedia

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