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Threefolds of P^5 with one apparent quadruple point

Pietro De Poi
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Abstract

In this article we classify all the smooth threefolds of P^5 with an apparent quadruple point provided that the family of its 4-secant lines is an irreducible (first order) congruence. This is sufficient to conclude the classification of all the smooth codimension two varieties of P^n with one apparent (n-1)-point and with irreducible family of (n-1)-secant lines.

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Pietro De Poi. 2002-07-12. Threefolds of P^5 with one apparent quadruple point. https://doi.org/10.1081/agb-120018514

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