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Transactions of the American Mathematical Society

ISSN 1088-6850(online) ISSN 0002-9947(print)



On the topology and geometric construction of oriented matroids and convex polytopes

Authors: Jürgen Richter and Bernd Sturmfels
Journal: Trans. Amer. Math. Soc. 325 (1991), 389-412
MSC: Primary 05B35; Secondary 52B12
MathSciNet review: 994170
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Abstract: This paper develops new combinatorial and geometric techniques for studying the topology of the real semialgebraic variety $ \mathcal{R}(M)$ of all realizations of an oriented matroid $ M$ . We focus our attention on point configurations in general position, and as the main result we prove that the realization space of every uniform rank $ 3$ oriented matroid with up to eight points is contractible. For these special classes our theorem implies the isotopy property which states the spaces $ \mathcal{R}(M)$ are path-connected.

We further apply our methods to several related problems on convex polytopes and line arrangements. A geometric construction and the isotopy property are obtained for a large class of neighborly polytopes. We improve a result of M. Las Vergnas by constructing a smallest counterexample to a conjecture of G. Ringel, and, finally, we discuss the solution to a problem of R. Cordovil and P. Duchet on the realizability of cyclic matroid polytopes.

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Article copyright: © Copyright 1991 American Mathematical Society

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