Mnëv's universality theorem
In algebraic geometry, Mnëv's universality theorem is a result which can be used to represent algebraic (or semi algebraic) varieties as realizations of oriented matroids, a notion of combinatorics.[1][2][3]
Oriented matroids[]
For the purposes of Mnëv's universality, an oriented matroid of a finite subset is a list of all partitions of points in S induced by hyperplanes in . In particular, the structure of oriented matroid contains full information on the incidence relations in S, inducing on S a matroid structure.
The realization space of an oriented matroid is the space of all configurations of points inducing the same oriented matroid structure on S.
Stable equivalence of semialgebraic sets[]
For the purposes of Mnëv's Universality, the stable equivalence of semialgebraic sets is defined as follows.
Let U, V be semialgebraic sets, obtained as a disconnected union of connected semialgebraic sets
- ,
We say that U and V are rationally equivalent if there exist homeomorphisms defined by rational maps.
Let be semialgebraic sets,
- ,
with mapping to under the natural projection deleting last d coordinates. We say that is a stable projection if there exist integer polynomial maps
such that
The stable equivalence is an equivalence relation on semialgebraic subsets generated by stable projections and rational equivalence.
Mnëv's universality theorem[]
THEOREM (Mnëv's universality theorem)
Let V be a semialgebraic subset in defined over integers. Then V is stably equivalent to a realization space of a certain oriented matroid.
History[]
Mnëv's universality theorem was discovered by in his 1986 Ph.D. thesis.[4] It has numerous applications in algebraic geometry, due to Laurent Lafforgue, Ravi Vakil and others, allowing one to construct moduli spaces with arbitrarily bad behaviour.
Notes[]
- Universality Theorem, a lecture of Nikolai Mnëv (in Russian).
- Nikolai E. Mnëv, The universality theorems on the classification problem of configuration varieties and convex polytopes varieties (pp. 527–543), in "Topology and geometry: Rohlin Seminar." Edited by O. Ya. Viro. Lecture Notes in Mathematics, 1346. Springer-Verlag, Berlin, 1988.
- Vakil, Ravi (2006), "Murphy's Law in algebraic geometry: Badly-behaved deformation spaces", Inventiones Mathematicae, 164 (3): 569–590, arXiv:math/0411469, Bibcode:2006InMat.164..569V, doi:10.1007/s00222-005-0481-9, S2CID 7262537.
- Richter-Gebert, Jürgen (1995), "Mnëv's Universality Theorem Revisited", Séminaire Lotharingien de Combinatoire, B34h: 15
- Jürgen Richter-Gebert The universality theorems for oriented matroids and polytopes, Contemporary Mathematics 223, 269–292 (1999).
References[]
- ^ Mnev, N. E. (1988), "The universality theorems on the classification problem of configuration varieties and convex polytopes varieties", Topology and Geometry — Rohlin Seminar, Lecture Notes in Mathematics, vol. 1346, Springer Berlin Heidelberg, pp. 527–543, doi:10.1007/bfb0082792, ISBN 9783540502371
- ^ Sturmfels, Bernd; Gritzmann, Peter, eds. (1991-06-26). Applied Geometry and Discrete Mathematics: The Victor Klee Festschrift. DIMACS Series in Discrete Mathematics and Theoretical Computer Science. Vol. 4. Providence, Rhode Island: American Mathematical Society. doi:10.1090/dimacs/004. ISBN 9780821865934.
- ^ Vershik, A. M. (1988), Topology of the convex polytopes' manifolds, the manifold of the projective configurations of a given combinatorial type and representations of lattices, Lecture Notes in Mathematics, vol. 1346, Springer Berlin Heidelberg, pp. 557–581, doi:10.1007/bfb0082794, ISBN 9783540502371
- ^ "Nikolai Mnev Homepage". www.pdmi.ras.ru. Retrieved 2018-09-18.
- Real algebraic geometry
- Oriented matroids
- Theorems in algebraic geometry
- Theorems in combinatorics