Contents

Multiply transitive group action

The group action is sharply2-transitive if such ${\displaystyle g\in G}$ is unique.

A2-transitive group is a group such that there exists a group action that's 2-transitive and faithful. Similarly we can define sharply2-transitive group.

Equivalently, ${\displaystyle gx=w}$ and ${\displaystyle gy=z}$, since the induced action on the distinct set of pairs is ${\displaystyle g(x,y)=(gx,gy)}$.

The definition works in general with k replacing 2. Such multiply transitive permutation groups can be defined for any natural number k. Specifically, a permutation group G acting on n points is k-transitive if, given two sets of points a₁, ... a_k and b₁, ... b_k with the property that all the a_i are distinct and all the b_i are distinct, there is a group element ginG which maps a_itob_i for each i between 1 and k. The Mathieu groups are important examples.

Every group is trivially 1-transitive, by its action on itself by left-multiplication.

Let ${\displaystyle S_{n}}$ be the symmetric group acting on ${\displaystyle \{1,...,n\}}$, then the action is sharply n-transitive.

The group of n-dimensional homothety-translations acts 2-transitively on ${\displaystyle \mathbb {R} ^{n}}$.

The group of n-dimensional projective transforms almost acts sharply (n+2)-transitively on the n-dimensional real projective space ${\displaystyle \mathbb {RP} ^{n}}$. The almost is because the (n+2) points must be in general linear position. In other words, the n-dimensional projective transforms act transitively on the space of projective framesof${\displaystyle \mathbb {RP} ^{n}}$.

Every 2-transitive group is a primitive group, but not conversely. Every Zassenhaus group is 2-transitive, but not conversely. The solvable 2-transitive groups were classified by Bertram Huppert and are described in the list of transitive finite linear groups. The insoluble groups were classified by (Hering 1985) using the classification of finite simple groups and are all almost simple groups.

• Multiply transitive group

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