# Equidistance and Betweenness in Euclidean Plane Geometry

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Tarski axiomatized Euclidean plane geometry in first-order logic using two primitive relations: " lies between and ," written as , and " is as distant from as is from ," written as . This Demonstration shows that in plane Euclidean geometry, the relation is definable using relation , but the opposite is not true.

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Contributed by: Izidor Hafner (April 2018)

Open content licensed under CC BY-NC-SA

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## Details

Notation and definitions are from [2].

References

[1] A. Tarski, "What Is Elementary Geography?," *The Axiomatic Method: With Special Reference to Geometry and Physics* (L. Henkin, P. Suppes and A. Tarski, eds.), Amsterdam: North-Holland, 1959 pp. 16–29.

[2] A. Tarski and S. Givant, "Tarski's System of Geometry," *Bulletin of Symbolic Logic*, 5(2), 1999 pp. 175–214. www.math.ucla.edu/~asl/bsl/0502/0502-002.ps.

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