Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2008/ib/paper-1/10g/i/solution

The alternating group contains
The product of any two different nonidentity elements is the third, and each squares to the identity, so is a Klein four-group. Conjugation by a permutation replaces the labels in each cycle, preserving the property of being a product of two disjoint transpositions. Thus is a normal subgroup of . Its order is , strictly between and . is not simple.

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