Authors: Jenö Szirmai
Abstract
In the present paper we study $\SXR$ and $\HXR$ geometries, which are homogeneous Thurston 3-geometries.
We analyse the interior angle sums of geodesic triangles in both geometries and we prove that in $\SXR$ space it can be larger than or equal to $\pi$ and in $\HXR$ space the angle sums can be less than or equal to $\pi$.
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This proof is a new direct approach to the issue and it is based on the projective model of $\SXR$ and $\HXR$ geometries described by E. Moln\'ar in \cite{M97}.
Budapest University of Technology and
Economics Institute of Mathematics,
Department of Geometry,
Budapest, P. O. Box: 91, H-1521
E-mail:
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