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Nicolas Dutertre
Semi-algebraic neighborhoods of closed semi-algebraic sets
(Voisinages semi-algébriques d’ensembles semi-algébriques fermés)
Annales de l'institut Fourier, 59 no. 1 (2009), p. 429-458, doi: 10.5802/aif.2435
Article: subscription required (your ip address: 67.202.9.192) | Reviews MR 2514870 | Zbl 1174.14051
Class. Math.: 14P10, 14P25
Keywords: Tubular neighborhood, semi-algebraic sets, retraction, quasiregular approaching semi-algebraic function, quasiregular approaching semi-algebraic neighborhood

Résumé - Abstract

Given a closed (not necessarly compact) semi-algebraic set $X$ in $\mathbb{R}^n$, we construct a non-negative semi-algebraic ${\mathcal{C}}^2$ function $f$ such that ${X{=}f^{-1}(0)}$ and such that for $\delta >0$ sufficiently small, the inclusion of $X$ in $f^{-1}([0,\delta ])$ is a retraction. As a corollary, we obtain several formulas for the Euler characteristic of $X$.

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