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Published online by Cambridge University Press: 22 February 2019
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.
Supported by the European Research Council grant 338821, by ISF grant No. 181/16 and ISF grant No. 1382/15.
Supported by the Israel Science Foundation grants no. 1533/14 and 1254/18.