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Burnside's lemma

Let GG be a finite group that acts on a set XX. For each gg in GG let XgX^g denote the set of elements in XX that are fixed by gg. Then the number of orbits is

∣X/G∣=1∣G∣∑g∈G∣Xg∣.|X/G| = \frac{1}{|G|} \sum_{g\in G} |X^g|.

Problems

See also