Solution

ID: past-exam-of-the-building-infinite-groups-course-of-the-university-of-oxford/2011/3/a/solution

Let , with each a copy of . The permutation group acts on by
Define the permutation wreath product to be the semidirect product
Explicitly,
Writing for the element with entry in coordinate and identity elsewhere, and writing for , conjugation satisfies
Thus the top permutation group permutes the coordinate subgroups in exactly its given action. Distinct coordinate subgroups commute, including when itself is nonabelian.

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