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Let f be a homomorphism from G onto H with kernel K: f:Gk--->H. If S is any subgroup of H, let S*={x∈G: f(x) ∈ S}. Prove: S ≅S* / K

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Perhaps you can include a bit of your own thought on the problem. Many users here find it rude when questions are asked in the imperative. –  EuYu Nov 26 '12 at 1:42
Can you see that $K\subseteq S^*$? –  Berci Nov 26 '12 at 2:05

1 Answer 1

Hint: For a group $G$ and its normal subgroup $N$, the elements of the quotient group $G/N$ are basically those of $G$, but all $n\in N$ is identified with $1$, and as all the consequences of these we have that $g$ and $g'$ are equal as elements of $G/N$ iff $g'=gn$ for some $n\in N$.

Then apply the same to the subgroup $S$, and the required isomorphism is basically given by $f$.

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