Displaying similar documents to “The irregularity of ruled surfaces in three dimensional projective space.”

Some examples of Gorenstein liaison in codimension three.

Robin Hartshorne (2002)

Collectanea Mathematica

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Gorenstein liaison seems to be the natural notion to generalize to higher codimension the well-known results about liaison of varieties of codimension 2 in projective space. In this paper we study points in P3 and curves in P4 in an attempt to see how far typical codimension 2 results will extend. While the results are satisfactory for small degree, we find in each case examples where we cannot decide the outcome. This examples are candidates for counterexamples to the hoped-for extensions...

Geometry of arithmetically Gorenstein curves in P.

Robin Hartshorne (2004)

Collectanea Mathematica

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We characterize the postulation character of arithmetically Gorenstein curves in P. We give conditions under which the curve can be realized in the form mH - K on some ACM surface. Finally, we complement a theorem by Watanabe by showing that any general arithmetically Gorenstein curve in P with arbitrary fixed postulation character can be obtained from a line by a series of ascending complete-intersection biliaisons.

A note on a theorem of Xiao Gang.

Margarita Mendes Lopes (2004)

Collectanea Mathematica

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In 1985 Xiao Gang proved that the bicanonical surface of a complex surface S of general type with p2(S) > 2 is not composed of a pencil. In this note a new proof of this theorem is presented.