Abstract
In this paper, we study the local structure of extremal contractionsf∶X→S from threefoldsX with only terminal singularities onto a surfaceS. If the surfaceS is nonsingular andX has a unique non-Gorenstein point on a fiber, we prove that either the linear system ¦−K X ¦, ¦−2K X ¦, or ¦−3K X ¦contains a “good” divisor.
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Translated from Itogi Nauki i Tekhniki, Seriya Sovremennaya Matematika i Ee Prilozheniya. Tematicheskie Obzory. Vol. 45, Algebraic Geometry-8, 1997.
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Prokhorov, Y.G. On extremal contractions from threefolds to surfaces: The case of one non-Gorenstein point and a nonsingular base surface. J Math Sci 95, 1986–1995 (1999). https://doi.org/10.1007/BF02169156
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DOI: https://doi.org/10.1007/BF02169156