Le Matematiche (Dipartimento di Matematica e Informatica, Università degli Studi di Catania)
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A deformation theory approach to linear systems with general triple point
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Experiments with the Gorenstein liaison
No full textWe give some experimental data of Gorenstein liaison, working with points in P^3 and curves in P^4 , to see how far the familiar situation of liaison, biliaison, and Rao modules of curves in P^3 will extend to subvarieties of codimension 3 in higher P^4
Projective moduli space of semistable principal sheaves for a reductive group
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On the cohomology and genus of projective curves
Get PDFWe discuss recent results on the possible pairs of degree and genus of projective curves and on the related problem of bounding the cohomology of curves
The usual Castelnuovo\u27s argument and special subhomaloidal systems of quadric
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On quadrisecant lines of threefolds in P^5
Get PDFWe study smooth threefolds of P^5 whose quadrisecant lines don\u27t fill up the space. We give a complete classification of those threefolds X whose only quadrisecant lines are the lines contained in X . Then we prove that, if X admits "true" quadrisecant lines, but they don\u27t fill up P^5 , then either X is contained in a cubic hypersurface, or it contains a family of dimension at least two of plane curves of degree at least four
Attempts to use the power of modern group theory in finite simple groups for calculating Galois groups
Get PDFThis is the text of my lectures in Catania (Sicily) in April 2001, and at a Group Theory Conference in Oberwohlfach (Germany) in April 1997. The Catania visit was in honor of the 60-th birthday of my good friend Sylvio Greco
On the osculatory behavior of surface scrolls
Get PDFA lower bound for the dimensions of the second osculating spaces to any surface scroll is given, relying on the special feature of osculating hyperplane sections to such surfaces. Moreover a class of counterexamples to the even dimensional part of a conjecture of Piene-Tai is provided
Dedekind different and type sequences
Get PDFLet R be a one-dimensional, local, Noetherian domain. We assume R analitycally irreducible and residually rational. Let ω be a canonical module of R such that R ⊆ ω ⊆ R and let θ_D := R : ω be the Dedekind different of R.Our purpose is to study how θ_D is involved in the type sequence of R and to compare the type sequence of R with the type sequence of θ_D (for the notion of type sequence we refer to [11], [1] and [13]). These relations yield some interesting consequences