An incidence-preserving transformation in which points and lines are transformed into their poles and polars. A Projective Geometry-like Duality Principle holds for reciprocation.

**References**

Coxeter, H. S. M. and Greitzer, S. L. ``Reciprocation.'' §6.1 in *Geometry Revisited.*
Washington, DC: Math. Assoc. Amer., pp. 132-136, 1967.

© 1996-9

1999-05-25