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arXiv 2302.01055math.AG
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正则几何中的逼近与同伦

Approximation and homotopy in regulous geometry

Wojciech Kucharz

摘要:

设X,Y是非奇异实代数集.一个映射fi:X-->Y称为k-正则的,其中k是非负整数,如果它是C^k类的,且fi对X的某个Zebriki开稠密子集的限制是正则映射.设Y是一致有理的,且k>0,我们证明了C^inf映射f:X-->Y可以用C^k拓扑中的k-正则映射逼近当且仅当f同伦于k-正则映射.一致有理实代数簇包括球面、Grassmannian曲面和实有理曲面,并且在非奇异中心爆破下是稳定的。进一步,设Y=S^p(单位p维球面),我们得到了C^k拓扑中k-正则映射对X到S^p的C^inf映射的逼近的几个新结果,其中k是非负的.

英文摘要:

Let X, Y be nonsingular real algebraic sets. A map fi:X-->Y is said to be k-regulous, where k is a nonnegative integer, if it is of class C^k and the restriction of fi to some Zariski open dense subset of X is a regular map. Assuming that Y is uniformly rational, and k>0, we prove that a C^inf map f:X-->Y can be approximated by k-regulous maps in the C^k topology if and only if f is homotopic to a k-regulous map. The class of uniformly rational real algebraic varieties includes spheres, Grassmannians and real rational surfaces, and is stable under blowing up nonsingular centers. Furthermore, Taking Y=S^p (the unit p-dimensional sphere), we obtain several new results on approximation of C^inf maps from X into S^p by k-regulous maps in the C^k topology, for k nonnegative.

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