arXiv subjects

Hamid Torabi

Publications and source records attributed to Hamid Torabi.

At least 19 recordsLinked to original sources

arXiv2025

On Targeted Complexity of Discrete Motion

In this paper, we study targeted simplicial complexity $TC(K, L)$ introduced for situations where the configuration space possesses a simplicial structure $K$ together with a set of configurations $L$ as the target of motion. This type of complexity admits smaller values than the discrete version $TC(K)$. We then demonstrate that targeted simplicial complexity is strongly homotopy invariant and it varies between simplicial LS-categories of $K$ and $K \prod K$. Utilizing this information, we calculate targeted simplicial complexity for cases such as strongly collapsible complexes being equal to zero and for categoriacl subcomplex $L$, $TC(K,L) = scat(K)$. Moreover, we compare targeted simplicial complexity with relative topological complexity getting $TC(|K|, |L|) \le TC (K,L)$ where $|\cdot|$ denotes the geometric realization functor, and they are equal in certain cases, such as arbitrary wedges of triangulated circles. Also we define targeted $m$-step simplicial complexity of motions $TC_m(K,L)$ by using $m$-paths, paths whose length is smaller than or equal to $m$, to solve the problems of motion where the robot needs to be charged or repaired after $m$-steps. For $m$-step simplicial complexity a new invariance holds, which we call $m$-homotopy invariance introduced by $m$-paths. Finally we compare targeted $m$-step simplicial complexity with $m$-simplicial category $Scat_m$ to obtain some lower and upper bounds and then we prove the sequence of inequalities $scat_{m}(K)\leq TC_{m}(K,L) \le TC_{m}(K) \leq scat_{[\frac{m}{2}]}(K\prod K)$.

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arXiv2024

Discrete homotopic distance between Lipschitz maps

In this paper, we investigate a discrete version of the homotopic distance between two $s$-Lipschitz maps for $s \geq 0$. This distance is defined by specifying a step length $r$ to which some homotopy relation corresponds. In spaces with a significant number of holes, where no continuous homotopy exist and the homotopic distance equals infinite, the discrete homotopic distance provides a meaningful classification by effectively ignoring smaller holes. We show that the discrete homotopic distance $D_r$ generalizes key concepts such as the discrete Lusternik-Schnirelmann category $\text{cat}_r$ and the discrete topological complexity $\text{TC}_r$. Furthermore, we prove that $D_r$ is invariant under discrete homotopy relations. This approach offers a flexible framework for classifying $s$-Lipschitz maps, loops, and paths based on the choice of $r$.

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arXiv2024

A Discrete Topological Complexity of Discrete Motion Planning

In this paper we generalize the discrete r-homotopy to the discrete (s, r)-homotopy. Then by this notion, we introduce the discrete motion planning for robots which can move discreetly. Moreover, in this case the number of motion planning, called discrete topological complexity, required for these robots is reduced. Then we prove some properties of discrete topological complexity; For instance, we show that a discrete motion planning in a metric space X exists if and only if X is a discrete contractible space. Also, we prove that the discrete topological complexity depends only on the strictly discrete homotopy type of spaces.

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arXiv2022

On Topological Homotopy Groups and Relation to Hawaiian Groups

By generalizing the whisker topology on the $n$th homotopy group of pointed space $(X, x_0)$, denoted by $\pi_n^{wh}(X, x_0)$, we show that $\pi_n^{wh}(X, x_0)$ is a topological group if $n \ge 2$. Also, we present some necessary and sufficient conditions for $\pi_n^{wh}(X,x_0)$ to be discrete, Hausdorff and indiscrete. Then we prove that $L_n(X,x_0)$ the natural epimorphic image of the Hawaiian group $\mathcal{H}_n(X, x_0)$ is equal to the set of all classes of convergent sequences to the identity in $\pi_n^{wh}(X, x_0)$. As a consequence, we show that $L_n(X, x_0) \cong L_n(Y, y_0)$ if $\pi_n^{wh}(X, x_0) \cong \pi_n^{wh}(Y, y_0)$, but the converse does not hold in general, except for some conditions. Also, we show that on some classes of spaces such as semilocally $n$-simply connected spaces and $n$-Hawaiian like spaces, the whisker topology and the topology induced by the compact-open topology of $n$-loop space coincide. Finally, we show that $n$-SLT paths can transfer $\pi_n^{wh}$ and hence $L_n$ isomorphically along its points.

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arXiv2022

On Hawaiian homology groups

In this paper, we introduce a kind of homology which we call Hawaiian homology to study and classify pointed topological spaces. The Hawaiian homology group has advantages of Hawaiian groups. Moreover, the first Hawaiian homology group is isomorphic to the abelianization of the first Hawaiian group for path-connected and locally path-connected topological spaces. Since Hawaiian homology has concrete elements and abelian structure, its calculations are more routine. Thus we use Hawaiian homology groups to compare Hawaiian groups, and then we obtain some information about Hawaiian groups of some wild topological spaces.

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arXiv2021

On quasi-small loop groups

In this paper, we study some properties of homotopical closeness for paths. We define the quasi-small loop group as the subgroup of all classes of loops that are homotopically close to null-homotopic loops, denoted by $π_1^{qs} (X, x)$ for a pointed space $(X, x)$. Then we prove that, unlike the small loop group, the quasi-small loop group $π_1^{qs}(X, x)$ does not depend on the base point, and that it is a normal subgroup containing $π_1^{sg}(X, x)$, the small generated subgroup of the fundamental group. Also, we show that a space $X$ is homotopically path Hausdorff if and only if $π_1^{qs} (X, x)$ is trivial. Finally, as consequences, we give some relationships between the quasi-small loop group and the quasi-topological fundamental group.

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arXiv2018

On Generalized Covering Groups of Topological Groups

It is well-known that a homomorphism p between topological groups K, G is a covering homomorphism if and only if p is an open epimorphism with discrete kernel. In this paper we generalize this fact, in precisely, we show that for a connected locally path connected topological group G, a continuous map p is a generalized covering if and only if K is a topological group and p is an open epimorphism with prodiscrete (i.e, product of discrete groups) kernel. To do this we first show that if G is a topological group and H is any generalized covering subgroup of fundamental group of G, then H is as intersection of all covering subgroups, which contain H. Finally, we show that every generalized covering of a connected locally path connected topological group is a fibration.

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arXiv2018

On Topologized Fundamental Group and covering spaces of topological groups

In this paper, we show that every topological group is a strong small loop transfer space at the identity element. This implies that the quasitopological fundamental group of a connected locally path connected topological group is a topological group. Also, we show that every covering space of a connected locally path connected topological group is a topological group and its covering map is homomorphism.

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arXiv2017

On Topologized Fundamental Groups with Small Loop Transfer Viewpoints

In this paper, by introducing some kind of small loop transfer spaces at a point, we study the behavior of topologized fundamental groups with the compact-open topology and the whisker topology, $π_{1}^{qtop}(X,x_{0})$ and $π_{1}^{wh}(X,x_{0})$, respectively. In particular, we give necessary or sufficient conditions for coincidence and being topological group of these two topologized fundamental groups. Finally, we give some examples to show that the reverse of some of these implications do not hold, in general.

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arXiv2017

On a Van Kampen Theorem for Hawaiian Groups

The paper is devoted to study the $n$th Hawaiian group $\mathcal{H}_n$, $n \ge 1$, of the wedge sum of two spaces $(X,x_*) = (X_1, x_1) \vee (X_2, x_2)$. Indeed, we are going to give some versions of the van Kampen theorem for Hawaiian groups of the wedge sum of spaces. First, among some results on Hawaiian groups of semilocally strongly contractible spaces, we present a structure for the $n$th Hawaiian group of the wedge sum of CW-complexes. Second, we give more informative structures for the $n$th Hawaiian group of the wedge sum $X$, when $X$ is semilocally $n$-simply connected at $x_*$. Finally, as a consequence, by generalizing the well-known Griffiths space for dimension $n\geq 1$, we give some information about the structure of Hawaiian groups of Griffiths spaces at any points.

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arXiv2016

When Is a Local Homeomorphism a Semicovering map?

In this paper, by reviewing the concept of semicovering maps, we present some conditions under which a local homeomorphism becomes a semicovering map. We also obtain some conditions under which a local homeomorphism is a covering map.

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arXiv2016

On Semicovering, Subsemicovering and Subcovering Maps

In this paper, by reviewing the concept of subcovering and semicovering maps, we extend the notion of subcovering map to subsemicovering map. We present some necessary or sufficient conditions for a local homeomorphism to be a subsemicovering map. Moreover, we investigate the relationship between these conditions by some examples. Finally, we give a necessary and sufficient condition for a subsemicovering map to be semicovering.

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arXiv2016

On Subgroups of Topologized Fundamental Groups and Generalized Coverings

In this paper, we are interested in study subgroups of topologized fundamental groups and their influences on generalized covering maps. More precisely, we find some relationships between generalized covering subgroups and the other famous subgroups of the fundamental group equipped with the compact-open topology and the whisker topology. Moreover, we present some conditions under which generalized coverings, semicoverings and coverings are equal.

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arXiv2014

On topological fundamental groups of quotient spaces

Let $p:X\rightarrow X/A$ be a quotient map, where $A$ is a subspace of $X$. We explore conditions under which $p_*(π_1^{qtop}(X,x_0))$ is dense in $π_1^{qtop}(X/A,*))$, where the fundamental groups enjoy the natural quotient topology inherited from the loop space and $p_*$ is the induced continuous homomorphism by the quotient map $p$. Also, we give some applications to find out some properties for $π_1^{qtop}(X/A,*)$. In particular, we give some conditions in which $π_1^{qtop}(X/A,*)$ is an indiscrete topological group.

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arXiv2014

On locally 1-connectedness of quotient spaces and its applications to fundamental groups

Let $X$ be a locally 1-connected metric space and $A_1,A_2,...,A_n$ be connected, locally path connected and compact pairwise disjoint subspaces of $X$. In this paper, we show that the quotient space $X/(A_1,A_2,...,A_n)$ obtained from $X$ by collapsing each of the sets $A_i$'s to a point, is also locally 1-connected. Moreover, we prove that the induced continuous homomorphism of quasitopological fundamental groups is surjective. Finally, we give some applications to find out some properties of the fundamental group of the quotient space $X/(A_1,A_2,...,A_n)$.

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arXiv2013

On the Existence of Categorical Universal Coverings

In this paper, we study necessary and sufficient conditions for the existence of categorical universal coverings using open covers of a given space $X$. As some applications, first we present a generalized version of the Shelah Theorem (Mycielski's conjecture: If $X$ is a Peano continuum, then $π_1(X,x)$ is uncountable or $X$ has a simply connected universal covering) which states that a first countable Peano space has a categorical universal covering or has an uncountable fundamental group. Second, we prove that the one point union $X_1\vee X_2=\frac{{X_1}\cup {X_2}}{{x_1}\sim {x_2}}$ has a categorical universal covering if and only if both $X_1$ and $X_2$ have categorical universal coverings.

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arXiv2013

Topological fundamental groups and small generated coverings

This paper is devoted to study some topological properties of the SG subgroup, $π_1^{sg}(X,x)$, of the quasitopological fundamental group of a based space $(X,x)$, $\pt$, its topological properties as a subgroup of the topological fundamental group $π_1^τ(X,x)$ and its influence on the existence of universal covering of $X$. First, we introduce small generated spaces which have indiscrete topological fundamental groups and also small generated coverings which are universal coverings in the categorical sense. Second, we give a necessary and sufficient condition for the existence of the small generated coverings. Finally, by introducing the notion of semi-locally small generatedness we show that the quasitopological fundamental groups of semi-locally small generated spaces are topological groups.

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arXiv2012

On the Spanier Groups and Covering and Semicovering Spaces

For a connected, locally path connected space $X$, let $H$ be a subgroup of the fundamental group of $X$, $π_1(X,x)$. We show that there exists an open cover $\cal U$ of $X$ such that $H$ contains the Spanier group $π({\U},x)$ if and only if the core of $H$ in $π_1(X,x)$ is open in the quasitopological fundamental group $π_1^{qtop}(X,x)$ or equivalently it is open in the topological fundamental group $π_1^τ(X,x)$. As a consequence, using the relation between the Spanier groups and covering spaces, we give a classification for connected covering spaces of $X$ based on the conjugacy classes of subgroups with open core in $π_1^{qtop}(X,x)$. Finally, we give a necessary and sufficient condition for the existence of a semicovering. Moreover, we present a condition under which every semicovering of $X$ is a covering.

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