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image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Journal of Geometryarrow_drop_down
image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
Journal of Geometry
Article . 1997 . Peer-reviewed
License: Springer TDM
Data sources: Crossref
image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
zbMATH Open
Article . 1997
Data sources: zbMATH Open
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Point-regular geometries

Authors: Stroppel, Markus;

Point-regular geometries

Abstract

The author continues his investigation in Geom. Dedicata 46, No. 1, 47-60 (1993; Zbl 0783.51002) of how geometries can be reconstructed from their automorphism groups. In the paper under review he considers incidence structures \((P,{\mathcal L})\) that admit sharply point transitive groups \(G\) of automorphisms. In this case, \(P\) is identified with \(G\) and \(G\) acts on itself by the right regular action. For a set \({\mathbf S}\) of subgroups of \(G\) two systems of subsets of \(G\) are defined as follows. \({\mathcal L}^{\mathbf S}=\bigcup_{H\in{\mathbf S}}G/H\) is the union of all left coset spaces \(G/H\) for \(H\) in \({\mathbf S}\). Taking right cosets \(H\setminus G\) instead he likewise defines \(^{\mathbf S} {\mathcal L}=\cup_{H\in{\mathbf S}}H\setminus G\). In the latter case, \({\mathbf S}\) consists of the stabilizers of representatives for the \(G\)-orbits on \(^{\mathbf S}{\mathcal L}\) and the whole system of lines can be thought of as moving around some standard lines; this generalizes the familiar construction of translation planes. Various properties of these two systems are investigated in the first part of the paper. Whereas the group \(G\) acts on \(^{\mathbf S} {\mathcal L}\) in a natural way, this happens to be so for \({\mathcal L}^{\mathbf S}\) if and only if \({\mathbf S}\) is invariant under conjugation (and then \(^{\mathbf S} {\mathcal L}={\mathcal L}^{\mathbf S}\)). One obtains a linear space in both situations if and only if \({\mathbf S}\) forms a group partition of \(G\), that is, every non-identity element of \(G\) is in exactly one subgroup contained in \({\mathbf S}\). Furthermore, \((G,^{\mathbf S}{\mathcal L})\) always is a sketched geometry. In fact, it is shown that every point-regular sketched geometry can be represented in this form for some collection \({\mathbf S}\) of subgroups. In the second part the author applies his method to topological planes where the point set \(P\) is a topological manifold. In this case, the regular action of a locally compact, \(\sigma\)-compact group \(G\) on \(P\) is equivalent to the right regular action and \(G\) and \(P\) are homeomorphic. In particular, the author looks at the construction of arc planes by \textit{H. Groh} [Abh. Math. Semin. Univ. Hamburg 48, 171-202 (1979; Zbl 0415.51007)] and at stable planes. He generalizes a result of \textit{H. Groh} [loc. cit.] in characterising arcs \(A\) in \((G,^{\mathbf S} {\mathcal L})\), \({\mathbf S}\) a group partition, for which \((G,^{\mathbf S} {\mathcal L}(A))\) is a linear space where \(^{\mathbf S} {\mathcal L}(A)\) is obtained from \(^{\mathbf S} {\mathcal L}\) by deleting all lines, i.e., cosets \(Hg\) for \(H\in{\mathbf S}\) and \(g\in G\), for which \(AA^{-1}\) intersects \(H\) in more than the identity element (this gives a set of `slopes' for \(A\)) and adding all orbits of \(A\) under \(G\). Finally the author collects examples of point-regular actions on stable planes to illustrate how his construction may be used in the study of such planes.

Keywords

Incidence groups, group partition, Homomorphism, automorphism and dualities in linear incidence geometry, Linear incidence geometric structures with parallelism, incidence group, arc plane

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This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
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