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**Greg Hjorth** (14 June 1963 – 13 January 2011) was an Australian Professor of Mathematics,^{[1]} chess International Master (1984) and joint (with Ian Rogers) Commonwealth Champion in 1983.^{[2]} He worked in the field of mathematical logic.^{[3]}^{[4]}

Greg Hjorth | |
---|---|

Born | Melbourne, Australia | 14 June 1963

Died | 13 January 2011 Melbourne, Australia | (aged 47)

Nationality | Australian |

Known for | Hjorth's theory of turbulence |

Awards | First Sacks Prize from the Association for Symbolic Logic (ASL) (1993); Sloan Foundation Fellowship 1998; An invitation to the International Congress of Mathematicians (1998); The Karp Prize of the ASL (2003); Invited key speaker to the Alfred Tarski Lectures at UC Berkeley |

Scientific career | |

Fields | Mathematics, set theory, logic |

Institutions | University of Melbourne University of California |

Doctoral advisor | William Hugh Woodin |

Hjorth came second in the 1980 Australian Chess Championship, at the age of 16.^{[5]} He won the Doeberl Cup in Canberra in 1982, 1985 and 1987, and played for Australia in the Chess Olympiads of 1982, 1984 and 1986.^{[6]}

According to Chessmetrics, his best single performance was at the 1984 British Chess Championship, where he scored 4/7 against 2551-rated opposition, for a performance rating of 2570.^{[7]}

Hjorth retired from most chess in the 1980s.

Hjorth earned his PhD in 1993, under the direction of W. Hugh Woodin, with a dissertation entitled *On the influence of second uniform indiscernible*. He held faculty positions at the University of California, Los Angeles and the University of Melbourne. University Of Melbourne has Greg Hjorth Memorial Prize (biennial scholarship is awarded to the most outstanding postgraduate thesis in mathematics, with preference given to areas of logic, set theory, measure theory or related topics passed by examiners within the previous two calendar years) named after him.^{[8]} Among his most important contributions to set theory was the so-called theory of *turbulence*, used in the theory of Borel equivalence relations.^{[9]}^{[10]} In 1998, he was an Invited Speaker of the International Congress of Mathematicians in Berlin.^{[11]}

Hjorth died suddenly of a heart attack in Melbourne, on 13 January 2011.

- G. Hjorth:
*Classification and Orbit Equivalence Relations*, Mathematical Surveys and Monographs,**75**, American Mathematical Society, Providence, Rhode Island, 2000.

**^**"In memoriam Greg Hjorth, Professor of Mathematics, 1963–2011 UCLA Department of Mathematics". Ucla.edu. Archived from the original on 10 April 2011. Retrieved 21 May 2011.**^**"The chess games of Greg Hjorth". ChessGames.com. Retrieved 21 May 2011.**^**Zach, Richard (28 January 2011). "Gregory Hjorth, 1963–2011". University of Calgary. Retrieved 21 May 2011.**^**"Personnel Department of Mathematics and Statistics: Professor Greg Hjorth". The University of Melbourne. Archived from the original on 2 January 2016. Retrieved 21 May 2011.**^**Rogers, Ian (1981),*Australian Chess – Into the Eighties*, Melbourne: Sun Books, ISBN 0-7251-0384-1**^**"Men's Chess Olympiads: Gregory Hjorth". OlimpBase. Retrieved 21 May 2011.**^**Sonas, Jeff. "Event Details: Amsterdam (OHRA), 1984". ChessMetrics. Retrieved 21 May 2011.**^**"Greg Hjorth Memorial Prize". 8 December 2018.**^**Hjorth, Greg (2000).*Classification and Orbit Equivalence Relations*. American Mathematical Soc. ISBN 978-0-8218-2002-5.**^**Hjorth, Greg (December 2002). "A dichotomy theorem for turbulence".*Journal of Symbolic Logic*.**67**(4): 1520–1540. doi:10.2178/jsl/1190150297. ISSN 0022-4812. S2CID 40510835.**^**Hjorth, Greg (1998). "When is an equivalence relation classifiable?".*Doc. Math. (Bielefeld) Extra Vol. ICM Berlin, 1998, vol. II*. pp. 23–32.

- Greg Hjorth's webpage at UCLA
- Greg Hjorth player profile and games at Chessgames.com
- Chessmetrics Player Profile: Greg Hjorth
- IM Greg Hjorth interviewed by FM Grant Szuveges