
doi: 10.1007/bf01223528
A point P is said to be a neighbour of a point Q if P and Q are incident with two distinct lines m and \(\ell\) (in symbols \(P\sim Q)\). \(P\sim \ell\) means P is a neighbour of some point of \(\ell.\) Let \(\ell\) and m be two lines, and let \(U\) be a point such that \(UI\ell\), \(U\nsim m\) (for the symbol ''I'' and the other special notions see \textit{C. Baker, N. D. Lane} and \textit{J. W. Lorimer}: J. Geom. 19, 8-42 (1982; Zbl 0505.51017). Then \(\frac{U}{\bigwedge}(\ell \to m)=\{(X,X')| XI\ell,\quad X'Im;X,X',U\quad collinear\}\) is called a projective relation. If \(p\nsim \ell\), then the map \(\ell \to^{p}m\) (X\(\rightsquigarrow PX\wedge m)\) is a bijective projective relation called a perspectivity. The projective relation \(\frac{U}{\bigwedge}\) is said to preserve order if it has the following property: for any W,X,Y,ZI\(\ell\) such that W,X,Y\(\nsim U\) and WX\(| YZ\) (the pair W, X separates the pair Y, Z) with (W,W'),(X,X'),(Y,Y'),(Z,Z')\(\in \frac{U}{\bigwedge}\) then either W'X'\(| Y'Z'\) or two or more of W',X',Y',Z' are equal. A projective Hjelmslev plane (PH) is called a preordered (ordered) PH- plane if all perspectivities \(\ell \to^{U}m\) (all projective relations \(\frac{U}{\bigwedge})\) preserve order. The following theorem is proved: A preordered uniform PH-plane is ordered.
Ordered geometries (ordered incidence structures, etc.), projective relation, perspectivity, preordered uniform projective Hjelmslev plane, preserve order, Topological linear incidence structures
Ordered geometries (ordered incidence structures, etc.), projective relation, perspectivity, preordered uniform projective Hjelmslev plane, preserve order, Topological linear incidence structures
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