Suppose $\Gamma$ is a simple graphgraph and $G=Aut(\Gamma)$$G=\mathrm{Aut}(\Gamma)$ is the automorphism group of $\Gamma$. If $G$ stabilizes a subgraph $\Gamma_1$,, and $G_0$ is the kernelpoint-wise stabiliser of the set $V(\Gamma_1)$ w.r.t. the action of $G$ on $\Gamma_1$$V(\Gamma)$, that is, $G_0=\cap_{x\in V(\Gamma_1)}Stab_G(x) $$G_0=\cap_{x\in V(\Gamma_1)}\ \mathrm{Stab}_G(x) $ and $G_1=Aut(\Gamma_1)$$G_1=\mathrm{Aut}(\Gamma_1)$, is it true that $G$ is the semidirect product of $G_0$ and $G_1$?
Rather light stylistic improvements. One mathematical change: it seems wrong to me that the OP spoke of the 'kernel of the action on the vertex set of the graph whose vertex set is stabilized'. My new formulation seems standard, and what the OP really means.
Peter Heinig
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