# Finite index normal subgroup in a normalised union of two groups. [duplicate]

Possible Duplicate:
Existence of simultaneously normal finite index subgroups

$G$ is a group, $A$ and $B$ are two subgroups of $G$. Let $H$ be a subgroup of $A\cap B$ which is of finite index in both $A$ and $B$. Does $H$ has a subgroup of finite index which is normal in both $A$ and $B$?

Edit : In view of the negative answer pointed below, let me add the additional requirement that the union $A\cup B$ be normalised by $G$.

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## marked as duplicate by Gjergji Zaimi, HJRW, Mark Sapir, Greg Kuperberg, Simon ThomasNov 17 '11 at 15:05

This question was marked as an exact duplicate of an existing question.

Thanks for the link ! – Drike Nov 17 '11 at 15:25
@Gjergji Zaimi Could this question be opened again, or should I open a new question? – Drike Nov 19 '11 at 6:37