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As is well known, the Lefschetz theorems for the \'etale fundamental group of SGA1 do not hold. We fill a small gap in the literature showing they do for tame coverings. Let $X$ be a regular projective variety over a field $k$, and let…

Algebraic Geometry · Mathematics 2015-09-29 Hélène Esnault , Lars Kindler

We consider isometric immersions of complete connected Riemannian manifolds into space forms of nonzero constant curvature. We prove that if such an immersion is compact and has semi-definite second fundamental form, then it is an embedding…

Differential Geometry · Mathematics 2018-03-22 Ronaldo F. de Lima , Rubens L. de Andrade

We present the plactic algebra on an arbitrary alphabet set $A$ by row generators and column generators respectively. We give Gr\"{o}bner-Shirshov bases for such presentations. In the case of column generators, a finite Gr\"{o}bner-Shirshov…

Rings and Algebras · Mathematics 2014-10-06 L. A. Bokut , Yuqun Chen , Weiping Chen , Jing Li

In Part I of this article we generalize the Linearized Doubling (LD) approach, introduced in earlier work by NK, by proving a general theorem stating that if $\Sigma$ is a closed minimal surface embedded in a Riemannian three-manifold…

Differential Geometry · Mathematics 2022-12-06 Nikolaos Kapouleas , Peter McGrath

The analytic von Neumann regular closure $R(\Gamma)$ of a complex group algebra $\C\Gamma$ was introduced by Linnell and Schick. This ring is the smallest $*$-regular subring in the algebra of affiliated operators $U(\Gamma)$ containing…

Operator Algebras · Mathematics 2010-06-29 Gabor Elek

Utilizing an embedding theorem of Obraztsov we construct groups as described in the title. This provides an affirmative answer to a problem of D. O. Revin. The constructed groups also provide a negative answer to a question highlighted by…

Group Theory · Mathematics 2025-06-23 Samuel M. Corson

We prove group existence and structure theorems in a general setting of tame topological theories. More precisely, we identify a linear/non-linear dividing line -- called topological 1-basedness -- among the class of t-minimal theories with…

Logic · Mathematics 2025-08-27 Benjamin Castle , Assaf Hasson , Will Johnson

We augment the body of existing results on embedding finite semigroups of a certain type into 2-generator finite semigroups of the same type. The approach adopted applies to finite semigroups the idempotents of which form a band and also to…

Group Theory · Mathematics 2019-01-25 Peter M. Higgins

The Heisenberg groups are examples of sub-Riemannian manifolds homeomorphic, but not diffeomorphic to the Euclidean space. Their metric is derived from curves which are only allowed to move in so-called horizontal directions. We report on…

Metric Geometry · Mathematics 2018-10-19 Armin Schikorra

In this paper, we prove two structure theorems for twisted Chevalley groups $G_\sigma (R)$ over a commutative ring $R$ with unity. The first theorem concerns the normality of $E'_\sigma (R,J)$, the elementary congruence subgroups at level…

Group Theory · Mathematics 2025-07-29 Shripad M. Garge , Deep H. Makadiya

We show that each classical pseudoriemann symmetric space G/H can be realized as space of pairs of complementary subspaces in a linear space. For each classical symmetric space we construct an open embedding to a grassmannian or to a…

Differential Geometry · Mathematics 2013-01-15 Yu. A. Neretin

The classical integral localization formula for equivariantly closed forms (Theorem 7.11 in [BGV]) is well-known and requires the acting Lie group to be compact. It is restated here as Theorem 2. In this article we extend this result to…

Differential Geometry · Mathematics 2007-09-23 Matvei Libine

Graph Neural Networks (GNNs) are emerging machine learning models on graphs. Although sufficiently deep GNNs are shown theoretically capable of fully preserving graph structures, most existing GNN models in practice are shallow and…

Machine Learning · Computer Science 2020-06-09 Ziwei Zhang , Peng Cui , Jian Pei , Xin Wang , Wenwu Zhu

Understanding how singularities behave under small perturbations is a central theme in singularity theory. In this paper we establish sufficient conditions for families of analytic function-germs on a germ of a complex analytic space to…

Algebraic Geometry · Mathematics 2025-12-04 R. Giménez Conejero , Andreas Lind , Aurélio Menegon

Let $G$ be a simple exceptional algebraic group of adjoint type over an algebraically closed field of characteristic $p>0$ and let $X = {\rm PSL}_{2}(p)$ be a subgroup of $G$ containing a regular unipotent element $x$ of $G$. By a theorem…

Group Theory · Mathematics 2019-04-16 Timothy C. Burness , Donna M. Testerman

We show that any embedding of the level-k diamond graph of Newman and Rabinovich into $L_p$, $1 < p \le 2$, requires distortion at least $\sqrt{k(p-1) + 1}$. An immediate consequence is that there exist arbitrarily large n-point sets $X…

Functional Analysis · Mathematics 2007-05-23 J. R. Lee , A. Naor

Let $G$ be either the Grigorchuk $2$-group or one of the Gupta-Sidki $p$-groups. We give new upper bounds for the diameters of the quotients of $G$ by its level stabilisers, as well as other natural sequences of finite-index normal…

Group Theory · Mathematics 2017-03-20 Henry Bradford

In this note we give a short and elementary proof of a more general version of Whitney's theorem that 3-connected planar graphs have a unique embedding in the plane. A consequence of the theorem is that cubic plane graphs cannot be embedded…

Combinatorics · Mathematics 2020-06-04 Gunnar Brinkmann

We show that Baumslag-Solitar groups are virtually 2-avoidable, that is, they admit finite index subgroup whose first homology is devoid of $\mathbb{Z}_2$ summand. We also prove virtual 2-avoidability for some other classes of one-relator…

Group Theory · Mathematics 2025-04-21 Satyanath Howladar

We construct several families of minimum genus embeddings of dense graphs using index 2 current graphs. In particular, we complete the genus formula for the octahedral graphs, solving a longstanding conjecture of Jungerman and Ringel, and…

Combinatorics · Mathematics 2023-06-26 Timothy Sun