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Threefolds with one apparent double point

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Abstract

The number of apparent double points of an irreducible projective variety X of dimension n in \(\mathbb {P}^{2n+1}\) is the number of secant lines to X passing through a general point of \(\mathbb {P}^{2n+1}\). This classical notion dates back to Severi. Smooth threefolds having one apparent double point have been classified in 2004 by Ciliberto, Mella and Russo. This paper presents examples and a partial classification of singular threefolds having one apparent double point.

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Acknowledgments

The author would like to thank his Ph.D. advisor Prof. Ciro Ciliberto for the patience, dedication and for the important suggestions on this paper.

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Correspondence to Vitalino Filho Cesca.

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Cesca, V.F. Threefolds with one apparent double point. Rend. Circ. Mat. Palermo, II. Ser 65, 255–272 (2016). https://doi.org/10.1007/s12215-016-0231-4

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