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Published online by Cambridge University Press: 13 August 2021
A permutation group G on a set A is ${\kappa }$-homogeneous iff for all
$X,Y\in \bigl [ {A} \bigr ]^ {\kappa } $ with
$|A\setminus X|=|A\setminus Y|=|A|$ there is a
$g\in G$ with
$g[X]=Y$. G is
${\kappa }$-transitive iff for any injective function f with
$\operatorname {dom}(f)\cup \operatorname {ran}(f)\in \bigl [ {A} \bigr ]^ {\le {\kappa }} $ and
$|A\setminus \operatorname {dom}(f)|=|A\setminus \operatorname {ran}(f)|=|A|$ there is a
$g\in G$ with
$f\subset g$.
Giving a partial answer to a question of P. M. Neumann [6] we show that there is an ${\omega }$-homogeneous but not
${\omega }$-transitive permutation group on a cardinal
${\lambda }$ provided
(i) ${\lambda }<{\omega }_{\omega }$, or
(ii) $2^{\omega }<{\lambda }$, and
${\mu }^{\omega }={\mu }^+$ and
$\Box _{\mu }$ hold for each
${\mu }\le {\lambda }$ with
${\omega }=\operatorname {cf}({\mu })<{{\mu }}$, or
(iii) our model was obtained by adding $(2^{\omega })^+$ many Cohen generic reals to some ground model.
For ${\kappa }>{\omega }$ we give a method to construct large
${\kappa }$-homogeneous, but not
${\kappa }$-transitive permutation groups. Using this method we show that there exist
${\kappa }^+$-homogeneous, but not
${\kappa }^+$-transitive permutation groups on
${\kappa }^{+n}$ for each infinite cardinal
${\kappa }$ and natural number
$n\ge 1$ provided
$V=L$.