Luc Illusie

Luc Illusie entered the École Normale Supérieure in 1959. At first a student of the mathematician Henri Cartan, he participated in the Cartan–Schwartz seminar of 1963–1964. In 1964, following Cartan's advice, he began to work with Alexandre Grothendieck, collaborating with him on two volumes of the latter's Séminaire de Géométrie Algébrique du Bois Marie. In 1970, Illusie introduced the concept of the cotangent complex.

A researcher in the Centre national de la recherche scientifique from 1964 to 1976, Illusie then became a professor at the University of Paris-Sud, retiring as emeritus professor in 2005.{{cite web| url=http://www.math.u-psud.fr/~illusie/| title=Luc Illusie| access-date=27 July 2016| website=Mathematics Department, Université Paris-Sud}} Between 1984 and 1995, he was the director of the arithmetic and algebraic geometry group in the department of mathematics of that university. {{Interlanguage link|Torsten Ekedahl|sv}} and Gérard Laumon are among his students.

In May 1971, Illusie defended a state doctorate ({{in lang|fr}} Thèse d’État) entitled "Cotangent complex; application to the theory of deformations" at the University of Paris-Sud, in front of a jury composed of

Alexander Grothendieck, Michel Demazure and Jean-Pierre Serre and presided by Henri Cartan.{{cite web |url=http://sites.mathdoc.fr/PMO/PDF/I_ILLUSIE-64.pdf |first=Luc |last=Illusie |title=Complexe cotangent; application à la théorie des déformations, Thèses présentées au Centre d'Orsay de l'Université Paris-Sud pour obtenir le grade de docteur es-sciences [Orsay – Série A, n° 749], Publications mathématiques d'Orsay 23, Bibliothèque de la Faculté des sciences Mathématique, 20415| year=1971}}

The thesis was published in French by Springer-Verlag as a two-volume book (in 1971{{cite book| first=Luc |last=Illusie| doi=10.1007/BFb0059052| title=Complexe Cotangent et Déformations I |volume=239|location=Berlin, Heidelberg, New York| publisher=Springer-Verlag| edition=First| series=Lecture Notes in Mathematics|issn=0075-8434|page=239| isbn=978-3-540-37001-7| year=1971}} & 1972{{cite book| first=Luc |last=Illusie| doi=10.1007/BFb0059052| title=Complexe Cotangent et Déformations II |volume=239|location=Berlin, Heidelberg, New York| publisher=Springer-Verlag| edition=First| series=Lecture Notes in Mathematics|issn=0075-8434|pages=283| isbn=978-3-540-37962-1| year=1972}}). The main results of the thesis are summarized in a paper in English (entitled "Cotangent complex and Deformations of torsors and group schemes") presented in Halifax, at Dalhousie University, in January 1971 as part of a colloquium on algebraic geometry. This paper, originally published by Springer-Verlag in 1972,{{cite encyclopedia |last=Illusie |first=Luc |author-link=Luc Illusie |editor1-last=Lawvere |editor1-first=F. William |editor1-link=William Lawvere|encyclopedia=Toposes, Algebraic Geometry and Logic |date=1972 |publisher=Springer |location=Berlin, Heidelberg, New York| series=Lecture Notes in Mathematics |volume=274 |doi=10.1007/BFb0073969|isbn= 978-3-540-37609-5 |pages=159–189|title=Toposes, Algebraic Geometry and Logic: Dalhousie University, Halifax, January 16-19, 1971 |chapter=Cotangent complex and deformations of torsors and group schemes }} also exists in a slightly extended version.

Illusie's construction of the cotangent complex generalizes that of Michel André{{cite book|last1=André|first1=Michel|title=Homologie des algèbres commutatives|date=1974|publisher=Springer-Verlag|page=287}} and Daniel Quillen{{cite journal|last1=Quillen|first1=Daniel|title=On the (co)-homology of commutative rings|journal=Proceedings of Symposia in Pure Mathematics|date=1970|volume=17|pages=65–87|doi=10.1090/pspum/017/0257068|isbn=9780821814178|doi-access=free}} to morphisms of ringed topoi. The generality of the framework makes it possible to apply the formalism to

various first-order deformation problems: schemes, morphisms of schemes,

group schemes and torsors under group schemes. Results concerning commutative

group schemes in particular were the key tool in Grothendieck's proof of his

existence and structure theorem for infinitesimal deformations of Barsotti–Tate groups,{{cite journal|last1=Illusie|first1=Luc|title=Déformations de groupes de Barsotti–Tate (d'après A. Grothendieck)|journal=Seminar on Arithmetic Bundles: The Mordell Conjecture (Paris, 1983/84). Astérisque|date=1985|volume=127|pages=151–198}} an ingredient in Gerd Faltings' proof of the Mordell conjecture. In Chapter VIII of the second volume of the thesis, Illusie introduces

and studies derived de Rham complexes.

Illusie has received the Langevin Prize of the French Academy of Sciences in 1977 and, in 2012, the Émile Picard Medal of the French Academy of Sciences for "his fundamental work on the cotangent complex, the Picard–Lefschetz formula, Hodge theory and logarithmic geometry".{{cite web|url=http://www.academie-sciences.fr/archivage_site/activite/prix/laureat_picard.pdf|title=Médaille Émile Picard (Mathématique): lauréats – Prix de l'Académie des sciences|website=French Academy of Sciences|date=3 October 2012|access-date=27 July 2016}}

• Complexe cotangent et déformations, Lecture Notes in Mathematics 239 et 283, Berlin and New York, Springer, 1971–1972.
• (ed.) Cohomologie ℓ-adique et fonctions L, Séminaire de Géométrie Algébrique du Bois-Marie 1965–66, SGA 5, dir. A. Grothendieck, Lecture Notes in Mathematics 589, Berlin and New York, Springer, 1977.
• (with Pierre Berthelot and Alexander Grothendieck), Théorie des intersections et théorème de Riemann–Roch, Séminaire de Géométrie Algébrique du Bois Marie 1966–67, SGA 6, Lecture Notes in Mathematics 225, Berlin and New York, Springer, 1971.
• "Complexe de de Rham–Witt et cohomologie cristalline", Annales Scientifiques de l'École Normale Supérieure, 1979, ser. 4, vol. 12, 4, pp. 501–661, url=http://archive.numdam.org/ARCHIVE/ASENS/ASENS_1979_4_12_4/ASENS_1979_4_12_4_501_0/ASENS_1979_4_12_4_501_0.pdf.
• (coed. with Jean Giraud and Michel Raynaud), Surfaces algébriques, Séminaire de géométrie algébrique d'Orsay 1976–78, Lecture Notes in Mathematics 868, Berlin and New York, Springer, 1981.
• (with Michel Raynaud), "Les suites spectrales ssociées au complexe de De Rham–Witt", Publ. Math. IHÉS, vol. 57, 1983, pp. 73–212.
• (with Pierre Deligne),"Relèvements modulo p² et décomposition du complexe de de Rham", Inv. math. (1987), vol. 89, pp. 247–270.
• "Sur la formule de Picard–Lefschetz", in Algebraic Geometry 2000, ed. Azumino (Hotaka), Advanced Studies in Pure Mathematics 36, 2002, pp. 249–268, Mathematical Society of Japan, Tokyo.

{{Reflist}}

• [http://www.math.u-psud.fr/~illusie/ Website at the Université Paris-Sud]
• {{MathGenealogy |id=13123 }}

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Category:1940 births

Category:Living people

Category:École Normale Supérieure alumni

Category:Algebraic geometers

Category:20th-century French mathematicians

Category:University of Paris alumni