[Event "IBM"]
[Site "Amsterdam"]
[Date "1971.07.16"]
[Round "4"]
[White "Ivkov, Borislav"]
[Black "Donner, Jan Hein"]
[Result "1/2-1/2"]

1. c4 Nf6 2. Nc3 e6 3. d4 Bb4 4. e3 c5 5. Ne2 d5 6. a3 Ba5 7. dxc5 dxc4 8. Qxd8+ Kxd8 9. Bd2 Nbd7 10. Ng3 Nxc5 11. Bxc4 Bc7 12. Rd1 a6 13. e4 Bd7 14. f4 Bc6 15. e5 Nfd7 16. Be3 Ke7 17. O-O Rhc8 18. Ba2 Bb6 19. Rfe1 Na4 20. Nxa4 Bxe3+ 21. Rxe3 Bxa4 22. Rd2 Rc1+ 23. Kf2 Rac8 24. Ne4 R8c2 25. Rxc2 Rxc2+ 26. Re2 Rxe2+ 27. Kxe2 Bc6 28. Ke3 Nb6 29. g3 Na4 30. b3 Bxe4 31. bxa4 Bc2 32. a5 Kd7 33. Kd4 Kc6 34. Bc4 Bf5 35. Be2 b6 36. g4 Bb1 37. Bxa6 bxa5 38. a4 h6 39. Bb5+ Kb6 40. h4 Bc2 41. Be8 Bd1 42. g5 hxg5 43. hxg5 Bg4 44. Bxf7 Bf5 45. Be8 g6 46. Bb5 Bc2 47. Bc4 Bf5 48. Bb3 Kc6 49. Bd1 Kb6 50. Bf3 Bc2 51. Bg4 Bb3 52. Bh3 Ba2 53. Bg2 Bb1 54. Kc4 Ba2+ 55. Kc3 Bb1 56. Kd4 Bc2 1/2-1/2