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A geometric description of Hazama's exceptional classes

Federica Galluzzi (2000)

Bollettino dell'Unione Matematica Italiana

Sia X una varietà abeliana complessa di tipo Mumford. In queste note daremo una descrizione esplicita delle classi eccezionali in B 2 X × X trovate da Hazama in [Ha] e le descriveremo geometricamente usando la grassmaniana delle rette di P 7 .

A Geometrical Construction for the Polynomial Invariants of some Reflection Groups

Sarti, Alessandra (2005)

Serdica Mathematical Journal

2000 Mathematics Subject Classification: Primary 20F55, 13F20; Secondary 14L30.We construct invariant polynomials for the reflection groups [3, 4, 3] and [3, 3, 5] by using some special sets of lines on the quadric P1 × P1 in P3. Then we give a simple proof of the well known fact that the ring of invariants are rationally generated in degree 2,6,8,12 and 2,12,20,30.

A groupoid characterization of Boolean algebras

Ivan Chajda (2004)

Discussiones Mathematicae - General Algebra and Applications

We present a groupoid which can be converted into a Boolean algebra with respect to term operations. Also conversely, every Boolean algebra can be reached in this way.

A groupoid characterization of orthomodular lattices

Ivan Chajda (2005)

Acta Universitatis Palackianae Olomucensis. Facultas Rerum Naturalium. Mathematica

We prove that an orthomodular lattice can be considered as a groupoid with a distinguished element satisfying simple identities.

A Hajós type result on factoring finite abelian groups by subsets. II

Keresztély Corrádi, Sándor Szabó (2010)

Commentationes Mathematicae Universitatis Carolinae

It is proved that if a finite abelian group is factored into a direct product of lacunary cyclic subsets, then at least one of the factors must be periodic. This result generalizes Hajós's factorization theorem.

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