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Usurpator [1]

a series of microcomputer chess programs by Harm Geert Muller (HGM), written in assembly for 6800 (Usurpator I) and 6502 (Usurpator II), published with listings as a regular book [2], also adapted for the Acorn Atom [3] [4] . Usurpator participated at eight Dutch Computer Chess Championships, with some gaps seven times in the period from 1981 until the 10th DOCCC, where Usurpator competed as matchbox computer [5] .

In 2005, 15 years later, Harm Geert Muller was invited by the CSVN to play the 25th DOCCC, and he rewrote Usurpator in C (Usurpator V), to run on a laptop, which was 10,000 times faster and had 100,000 times as much memory as the matchbox computer. Since the program was not designed to play that fast, it was thinking much too far ahead at the expense of immediate threats.


HGM's matchbox computer with a 65SC816 CPU for the purpose of running Usurpator. The matchbox competed three times at Dutch Computer Chess Championships, 1986 [6] , 1987 [7] , and 1990:

DOCCC 1990 - Firepower for a full board [8] Matchbox Design [9]

Re-Discovering Alpha-Beta

In that early times end of the 70s and early 80s when Harm Geert Muller developed his first programs, he had Alpha-Beta initially wrong in Usurpator I, since it omitted the deep cutoffs and was not passing alpha through the recursive call. After tracing the search tree HGM got aware and found out how to do the deep cutoffs, re-discovering Alpha-Beta by himself for Usurpator II [10] .

Photos & Games


DOCCC 2005: Harm Geert Muller and Stan Arts, Usurpator V - Neurosis [11] [12]
Usurpator V caused some thermic problems in the therefor upright standing Laptop

[Event "DOCCC 2005"]
[Site "Leiden NED"]
[Date "2005.11.11"]
[Round "02"]
[White "Usurpator V"]
[Black "Neurosis"]
[Result "0-1"]

1.e4 e5 2.Qh5 Nc6 3.Bc4 g6 4.Qe2 Nd4 5.Qd3 Nf6 6.c3 Nc6 7.Nf3 Bg7
8.b4 d5 9.Bxd5 Nxd5 10.exd5 Be6 11.h3 Bxd5 12.Qc2 e4 13.Ng1 Qg5
14.g4 e3 15.Rh2 Qf4 16.Rg2 Bxg2 17.dxe3 Qh2 18.Ne2 Qh1+ 19.Kd2 O-O-O+
20.Nd4 Ne5 21.Qa4 Nc4+ 22.Kc2 Be4+ 23.Kb3 Qd1+ 24.Kxc4 Bd3+
25.Kc5 Bf8# 0-1

See also


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