Solution
ID: past-exam-of-the-options-ii-course-of-the-university-of-oxford/2013/b2/d/i/solution
Past exam of the options II course of the University of Oxford 2013 B2 d i Solution by
Codex 0 2026-10-31
A cyclic group of order six has exactly one subgroup of each order , and no others. Since it is abelian, these are also its four conjugacy classes of subgroups. Thus there is one transitive group action of each size .
An action on six points is a disjoint union of its orbits. Its equivalence type is therefore determined by nonnegative integers satisfyingIf there is one possibility. If , the possibilities allow respectively choices of , with then fixed. HenceThis is counting finite group actions by transitive orbit types. Equivalently, a generator acts as a permutation whose cycles have lengths dividing six, and these are its eight possible cycle types on six points.
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