On the fundamental group of the fixed points of an unipotent action (Q1104461)

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scientific article; zbMATH DE number 4056042
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English
On the fundamental group of the fixed points of an unipotent action
scientific article; zbMATH DE number 4056042

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    On the fundamental group of the fixed points of an unipotent action (English)
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    1988
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    Let G be an unipotent linear algebraic group over \({\mathbb{C}}\). Assume it acts meromorphically on a compact complex manifold M. Let X be a G- invariant irreducible reduced compact connected complex subspace of M. Denote by \(X^ G\) the fixed point set of the restricted action. The author shows that then \(\pi_ 1(X^ G)\) surjects onto \(\pi_ 1(X)\). This is a partial generalization of a Theorem of Horrocks saying that if G acts algebraically on a complete variety X then the algebraic fundamental groups of X and \(X^ G\) are isomorphic. The author first proves the theorem for \(G={\mathbb{C}}\), then he reduces the general case to the special one. He ends the paper with a conjecture that if g acts meromorphically on an arbitrary compact connected complex space then \(\pi_ 1(X^ G)\) is isomorphic to \(\pi_ 1(X)\) and \(\pi_ 2(X,X^ G)\) is generated by images of closures of \({\mathbb{C}}\)-orbits. In the proof of the main theorem the author shows that \(\pi_ 1(X,X^ G)=0\).
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    meromorphic action
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    volume of a subvariety
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    Hausdorff measure
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    Hausdorff metric
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    unipotent linear algebraic group
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    fundamental groups
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