An inversive plane is a class of incidence structure in mathematics.
It may be axiomatised by taking two classes, "points" and "circles" (or "blocks") with the properties
- any three points lie on exactly one circle;
- if P and Q are points and c a circle with P on c and Q not, then there is exactly one circle e containing P and Q and intersecting c only in P;
- there are four points not all on the same circle.
The finite inversive planes are precisely the designs. Such a design is always a Steiner system.
Read more about Inversive Plane: Ovoids, Derived Designs and Extensions
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