- 342 名前：inciple, always work. In Case 1, take X=G/H. In Case 2, let H′=?g∈GgHg?1 be the normal core of H. It is easy to show that (since H has finite index), H′ is a finite index normal subgroup of G which is contained in H. Take X=G/H′ and f to be the quotient map.
answered Oct 26 '09 at 16:15
Pete L. Clark
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