Dual Structure
If we interchange the role of "points" and "lines" in
- C=(P,L,I)
the dual structure
- C*=(L,P,I*)
is obtained, where I* is the inverse relation of I. Clearly
- C**=C.
This is an abstract version of projective duality.
A structure C that is isomorphic to its dual C* is called self-dual.
Read more about this topic: Incidence Structure
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