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A generalisation of von Staudt’s theorem on cross-ratios

Published online by Cambridge University Press:  22 February 2019

YATIR HALEVI*
Affiliation:
Einstein Institute of Mathematics, Edmond J. Safra Campus, The Hebrew University of Jerusalem, Givat Ram 91904, Jerusalem, Israel
ITAY KAPLAN
Affiliation:
Einstein Institute of Mathematics, Edmond J. Safra Campus, The Hebrew University of Jerusalem, Givat Ram 91904, Jerusalem, Israel
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Abstract

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A generalisation of von Staudt’s theorem that every permutation of the projective line that preserves harmonic quadruples is a projective semilinear map is given. It is then concluded that any proper supergroup of permutations of the projective semilinear group over an algebraically closed field of transcendence degree at least 1 is 4-transitive.

Information

Type
Research Article
Copyright
Copyright © Cambridge Philosophical Society 2019