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On varieties of left distributive left idempotent groupoids

David Stanovský (2004)

Discussiones Mathematicae - General Algebra and Applications

We describe a part of the lattice of subvarieties of left distributive left idempotent groupoids (i.e. those satisfying the identities x(yz) ≈ (xy)(xz) and (xx)y ≈ xy) modulo the lattice of subvarieties of left distributive idempotent groupoids. A free groupoid in a subvariety of LDLI groupoids satisfying an identity xⁿ ≈ x decomposes as the direct product of its largest idempotent factor and a cycle. Some properties of subdirectly ireducible LDLI groupoids are found.

On Varieties of Literally Idempotent Languages

Ondřej Klíma, Libor Polák (2008)

RAIRO - Theoretical Informatics and Applications

A language L ⊆A* is literally idempotent in case that ua2v ∈ L if and only if uav ∈ L, for each u,v ∈ A*, a ∈ A. Varieties of literally idempotent languages result naturally by taking all literally idempotent languages in a classical (positive) variety or by considering a certain closure operator on classes of languages. We initiate the systematic study of such varieties. Various classes of literally idempotent languages can be characterized using syntactic methods. A starting example is the...

On volumes of arithmetic quotients of S O ( 1 , n )

Mikhail Belolipetsky (2004)

Annali della Scuola Normale Superiore di Pisa - Classe di Scienze

We apply G. Prasad’s volume formula for the arithmetic quotients of semi-simple groups and Bruhat-Tits theory to study the covolumes of arithmetic subgroups of S O ( 1 , n ) . As a result we prove that for any even dimension  n there exists a unique compact arithmetic hyperbolic n -orbifold of the smallest volume. We give a formula for the Euler-Poincaré characteristic of the orbifolds and present an explicit description of their fundamental groups as the stabilizers of certain lattices in quadratic spaces. We...

On weakly s -permutably embedded subgroups

Changwen Li (2011)

Commentationes Mathematicae Universitatis Carolinae

Suppose G is a finite group and H is a subgroup of G . H is said to be s -permutably embedded in G if for each prime p dividing | H | , a Sylow p -subgroup of H is also a Sylow p -subgroup of some s -permutable subgroup of G ; H is called weakly s -permutably embedded in G if there are a subnormal subgroup T of G and an s -permutably embedded subgroup H s e of G contained in H such that G = H T and H ∩ T ≤ H s e . We investigate the influence of weakly s -permutably embedded subgroups on the p -nilpotency and p -supersolvability of finite...

On weakly-supplemented subgroups and the solvability of finite groups

Qiang Zhou (2019)

Czechoslovak Mathematical Journal

A subgroup H of a finite group G is weakly-supplemented in G if there exists a proper subgroup K of G such that G = H K . In this paper, some interesting results with weakly-supplemented minimal subgroups or Sylow subgroups of G are obtained.

On weakly-supplemented subgroups of finite groups

Qingjun Kong (2019)

Czechoslovak Mathematical Journal

A subgroup H of a finite group G is weakly-supplemented in G if there exists a proper subgroup K of G such that G = H K . In this paper, some interesting results with weakly-supplemented minimal subgroups to a smaller subgroup of G are obtained.

On zeros of characters of finite groups

Jinshan Zhang, Zhencai Shen, Dandan Liu (2010)

Czechoslovak Mathematical Journal

For a finite group G and a non-linear irreducible complex character χ of G write υ ( χ ) = { g ∈ G ∣ χ ( g ) = 0 } . In this paper, we study the finite non-solvable groups G such that υ ( χ ) consists of at most two conjugacy classes for all but one of the non-linear irreducible characters χ of G . In particular, we characterize a class of finite solvable groups which are closely related to the above-mentioned question and are called solvable ϕ -groups. As a corollary, we answer Research Problem 2 in [Y. Berkovich and L. Kazarin: Finite...

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