On the Total Curvature of Semialgebraic Graphs
نویسنده
چکیده
We define the total curvature of a semialgebraic graph Γ ⊂ R as an integral K(Γ) = R Γ dμ, where μ is a certain Borel measure completely determined by the local extrinsic geometry of Γ. We prove that it satisfies the Chern-Lashof inequality K(Γ) ≥ b(Γ), where b(Γ) = b0(Γ) + b1(Γ), and we completely characterize those graphs for which we have equality. We also prove the following unknottedness result: if Γ ⊂ R is homeomorphic to the suspension of an n-point set, and satisfies the inequality K(Γ) < 2 + b(Γ), then Γ is unknotted. Moreover, we describe a simple planar graph G such that for any ε > 0 there exists a knotted semialgebraic embedding Γ of G in R satisfying K(Γ) < ε+ b(Γ).
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تاریخ انتشار 2008