Moufang plane
Builds on Projective planeCollinear points
Definition
A projective plane is a Moufang plane if it satisfies the little Desargues property for every line and every point on :
- let and be triangles with no vertex on , with , , , and with , , through ;
- suppose the points and lie on ;
- then the point also lies on .
Remarks
So three collinear intersection points are required only when the centre lies on the axis . Equivalently, every line of the plane is a translation line, that is, the group of elations with axis acts transitively on the points off . A projective plane is a Moufang plane exactly when it can be coordinatized by an alternative division ring.
Example: over a field is a Moufang plane. Check: Desargues's theorem holds in for all triangles in perspective, in particular when the centre lies on the axis.
By the Artin–Zorn theorem every finite alternative division ring is a field, so every finite Moufang plane is Desarguesian.
Non-example: the Hall plane of order is a finite non-Desarguesian plane. So by the previous sentence it is not a Moufang plane: the little Desargues property fails in it for some line and point .
Reading path
To understand this page from the ground up, read these 3 pages in order. The foundations come first.
Show the path as a graph
- no evidence level
- Collinear points concept
- Projective plane concept
- Moufang plane definition
Further reading
About this page
| Tag | P5HCD49REV |
|---|---|
| URI | m2://P5HCD49REV |
| Kind | definition |
| Writing | W0 stub |
| MSC | 51A35, 17D05 |
| Defines | Moufang plane |
| Uses | Projective plane, Collinear points |
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