Nolot

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Nolot is a chess test suite with 11 very difficult positions from real games. They were compiled by Pierre Nolot for the French chess magazine Gambisco and posted on the rec.games.chess Usenet group in 1994^[1]. Some of these positions are particularly hard to solve for chess engines.

1 Problem 1
2 Problem 2
3 Problem 3
4 Problem 4
5 Problem 5
6 Problem 6
7 Problem 7
8 Problem 8
9 Problem 9
10 Problem 10
11 Problem 11
12 References

[edit] Problem 1

Problem 1
Kasparov-Karpov, 1990 (Game 20) Chessgames.com

White to play: 26. Nxh6!!

26.Nxh6!! c3 (26... Rxh6 27.Nxd6 Qh5 (best) 28.Rg5! Qxd1 29.Nf7+ Kg8 30.Nxh6+ Kh8 31.Rxd1 c3 32.Nf7+ Kg8 33.Bg6! Nf4 34.Bxc3 Nxg6 35.Bxb4 Kxf7 36.Rd7+ Kf6 37.Rxg6+ Kxg6 38.Rxb7 +-) 27.Nf5! cxb2 28.Qg4 Bc8 (28... g6!? 29.Kh2! 29.Qd7 30.Nh4 Bc6 31.Nc5! dxc 32.Rxe6 Nf6 33.Nxg6+ Kg7 34.Qg5 Nbd5 35.Ne5 Kh8 36.Nxd7 +-) 29.Qh4+ Rh6 30.Nxh6 gxh6 31.Kh2! Qe5 32.Ng5 Qf6 33.Re8 Bf5 34.Qxh6 (missing a mate in 6: 34.Nf7+ Qxf7 35.Qxh6+ Bh7 36.Rxa8 Nf6 37.Rxf8 Qxf8 38.Qxf8+ Ng8 39.Qg7#) 34...Qxh6 35.Nf7+ Kh7 36.Bxf5+ Qg6 37.Bxg6+ Kg7 38.Rxa8 Be7 39.Rb8 a5 40.Be4+ Kxf7 41.Bxd5+ 1-0

The best Novag computer, the Diablo 68000, finds 26. Nxh6 after 7 months and a half (Pierre Nolot has let it run on the position for 14 months and one day, until a power failure stopped an analysis of over 80,000,000,000 nodes.) but for wrong reasons: it evaluates white's position as inferior and thinks this move would enable it to draw.

Today Gambit Tiger 2.0 for example can find it pretty fast:

1.Qd4 c3 2.Bxc3 Nxc3 3.Qxb4 Nxe4 4.Qxb7 Rb8 5.Qxb8 Qxb8 6.Bxe4 d5 7.Rb1
µ (-1.20) Depth: 12 00:00:09 6055kN
1.Nxh6 c3 2.Nf5 cxb2 3.Qg4 Rb8 4.Nxg7 Rg6 5.Qxg6 Qxg6 6.Rxg6 Bxg7 7.Nxd6
³ (-0.48) Depth: 12 00:00:21 14368kN
1.Nxh6 c3 2.Nf5 cxb2 3.Qg4 Rc8 4.Nxg7 Rg6 5.Nxe8 Rxg4 6.Rxg4 Rxe8 7.Rg6
µ (-0.74) Depth: 13 00:00:55 38455kN
1.Ne3 Rxe4 2.Bxe4 Qxe4 3.Nxd5 Qxd5 4.Qc1 Qf5 5.Qxh6+ Qh7 6.Qe6 Nd3 7.Re2 Nxb2 8.Rxb2
³ (-0.58) Depth: 13 00:01:30 62979kN
1.Ne3 Rxe4
³ (-0.58) Depth: 14 00:02:02 84941kN
1.Ne3 Nxe3 2.Rexe3 Bxe4 3.Qg4 Rg6 4.Qxe4 Qxe4 5.Bxe4 Rxg3 6.Rxg3 d5 7.Bf5 Re8 8.Bc3
³ (-0.30) Depth: 15 00:03:05 128968kN
1.Nxh6
² (0.32) Depth: 15 00:07:58 350813kN
With the next ply showing a clear advantage.

[edit] Problem 2

Problem 2
Bronstein - Ljubojevic, Petropolis itz 1973^[2]

White to play: 22. Rxc5!!

22.Rxc5!! Nxc5 23.Nf6+ Kh8 24.Qh4 Qb5+ (computers think there is perpetual check here, but...) 25.Ke3! 25... h5 26.Nxh5 Qxb3+ (26... d5+ 27.Bxd5 Qd3 28.Kf2 Ne4+ 29.Bxe4 Qd4+ 30.Kg2 Qxb2+ 31.Kh3 +-) and White won in 41 moves.

Today Deep Junior 8.ZX for example finds it very quickly (around 1 minute):

1.Kd1 Rac8 2.Bh6 Qb5 3.Rc3 Qf1+ 4.Kc2 Rc6 5.Bxf8
-+ (-2.11) Depth: 12 00:00:04 10422kN
1.Nxc5 Nxc5 2.Rxc5 Qxc5 3.e6 Rae8 4.e7 Nc8 5.Kf1 Nxd6 6.Bf6 b5
-+ (-2.10) Depth: 12 00:00:14 25054kN
1.Bf6!
µ (-1.35) Depth: 12 00:00:17 34601kN
1.Bf6 Qb5+ 2.Ke1 Bb4+ 3.Kf2 Bc5+
= (0.00) Depth: 12 00:00:20 34601kN
1.Bf6 Qb5+ 2.Ke1 Nxf6 3.Nxf6+ Kg7 4.Nh5+ gxh5 5.Qf6+ Kg8 6.Qg5+ Kh8 7.Qf6+
= (0.00) Depth: 15 00:01:01 130544kN
1.Rxc5!
= (0.15) Depth: 15 00:01:12 145875kN
1.Rxc5 Nxc5 2.Nf6+ Kh8 3.Qh4 Qb5+ 4.Ke3 h5 5.Nxh5 Qd3+ 6.Kf2 Ne4+ 7.fxe4 Qd4+ 8.Kf1 Qd3+ 9.Ke1 Qb1+ 10.Bd1
+- (2.18) Depth: 15 00:01:18 145875kN

[edit] Problem 3

Problem 3
Smaguine-Sahovic, Bienne 1990

White to play: 12. Nxg5!!

12.Nxg5!! Bxd1 13.Nxe6 Qb8 14.Nxg7!! Kf8 15.Bh6! Bg4 16.0-0+ 17.Kg8 17.Rf4 +-

White wins with a queen sac but black has defensive resources.

[edit] Problem 4

Problem 4
Bronstein - Kotov, candidates, Budapest 1950

White to play: 10. Nxe6!!

10.Nxe6!! Qxe6 11.Nd5 Kd8 12.Bg4 Qe5 13.f4 Qxe4 (13...Qxb2 stronger but not sufficient: 14.Bxd7 Bxd7 15.Rb1 Qa3 16.Nxf6 Bb5 17.Qd4 Qc5 18.Rfd1 +-) 14.Bxd7 Bxd7 15.Nxf6 gxf6 16.Bxf6+ Kc7 17.Bxh8 and Black resigned on move 27.

[edit] Problem 5

Problem 5
Spassky - Petrosian, w ch (19), Moscow 1969^[3]

White to play: 21. e5!!

21.e5!! dxe5 22.Ne4! Nh5 23.Qg6!? (stronger is 23.Qg4!! Nf4 24.Nf3 Qc7 25.Nh4 +- ) 23...exd4? 24.Ng5 1-0

[edit] Problem 6

Problem 6
Malaniuk - Ivanchuk, Moscow 1988^[4]

Black to play: 13. ... axb5!!

13... axb5!! offers a rook to keep the white queen out of play. 14.Qxa8 Bd4 15.Nxd4 cxd4 16.Qxb8 0-0! 17.Ke1 Qh4 18.g3 Qf6 19.Bf4 g5? (Ivantchouk found 19...d3! during post-game analysis.) 20.Rc1 exf4 21.Qxf4 Qd4 22.Rd1 bxc4 23.e5 Qc3+ 24.Rd2 Re8 25.Bxd3 cxd3 26.0-0 Nxe5 -+

Tasc R30 finds 19... d3! in 2 1/2 hours. 19... Bf5!! is even stronger than 19... d3.

[edit] Problem 7

Problem 7
Todorovic - Tosic, Arandjelovac, 1993

White to play: Rxd8+!!

1.Rxd8+!! Rxd8 (1...Kxd8 2.Ra7! Qe2 3.Qd4+ e8 4.h3 Qe1+ 5.Kh2 Rd8 6.Qc5 Qh4 7.Ba3 Rd7 8.Ra8+ Rd8 9.g3 1-0) 2.Ba3 Qe2 3.h3! Bd7 (better but still losing was 3...Qe1+ 4.Kh2 Qa5 5.Re7+ Kf8 6.Rd7+ Kg8 7.Bb4 Rxd7 8.Bxa5 +-) 4.Nf5! Qd1+ 5.Kh2 f6 6.e5xf6 1-0

The exchange sacrifice keeps control of the 7th rank. Genius 2 does better than the R30 on this one, but needs more than a month to find 1.Rxd8!!, even on a 90 MHz Pentium.

Fritz 9 play 1.Rxd8!! in 2 seconds.

[edit] Problem 8

Problem 8
Gufeld - Osnos, Koutaissi 1978^[5]

White to play: 24. Bxh7+!!

24.Bxh7+!! is natural, but Black has some defensive resources. 24...Kxh7 25.Qh5+ Kg8 26.Rd4! gxf6 27.Rg4+ Bg7 28.Qh6 Kf8 29.Rxg7! Rac8 (computers prefer 29...Be4 which also loses after 30.Rg4+ Ke7 31.Rxe4 Rad8 32.c4 Qa5 33.Rae1 +-) 30.Qh7 b5 31.Rd1 Bd5 32.c4 bxc4 33bxc4 1-0.

[edit] Problem 9

Problem 9
Weinstein - Elyoseph, Israel 1992

White to play: Ng5!!

1.Ng5!! hxg5 2.hxg5! Rac8 3.Nf6!! Nb8 (3...gxf6 still loses if white play precisely: 4.gxf6 4...Rfe8 (best) 5.Qh5 Rg8 6.Rxc5! Bg6! 7.Qh4 Bxc5 8.Be4 Ne7 9Kg2 Qd5 10.Bxd5 +-) 4.Qh5 Bxf6 5.gxf6 gxf6 6.Rxc5 Rxc5 7.Be4 f5 8.Kg2 Rg8 9.Rh1 Rg7 10.Bh6 Nd7 11.Bxg7+ Kxg7 12.Qxh7+ 1-0

[edit] Problem 10

Problem 10
Van der Wiel - Ribli, Amsterdam 1980^[6]

White to play: 15. Rxf7!!

15.Rxf7!! Rxf7 16.Bxf7 Kxf7 17.Qh5+ Kg8 16.Qe8+ Bf8 19.Nd5 Qxd4 20.Nxe7+ Kh8 21.Rf1 Qf6 22.Rxf6 and white won on move 29.

[edit] Problem 11

Problem 11
Teichmann - NN, Zurich 1920

White to play: Rxh6!!

Neishtadt's "Leçons de tactique" gives: "1.Rxh6!! the g pawn will be helped by the h pawn 1...Nxh6 (1...Rxh6 2.Bxf7+ Rxf7 3.g8Q+) 2.Qg5 Nf7 3.Qd8+!! Nxd8 4.h6 and there is nothing to prevent h6-h7+ 1-0"

But 4...Qd4!! 5.h7+ Kf7 6.g8Q+ Ke7 7.h8Q Kd6 8.Rg7 Qxd2!! 9.Qxd8 Rc5 10.Rxd7 Bxd7 11.Qxa8 Rb4 12.Qxa7 Qe1 13.Kb2 Qc3 1/2 as white cannot escape the black checks.