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Chemistry LibreTexts

Double coset

Let G be a group, and H and K be two subgroups of G. One says that the two elements g1 ∈ G and g2 ∈ G belong to the same double coset of G relative to H and K if there exist elements hi ∈ H and kj ∈ K such that:

g2 = hig1kj

The complex Hg1K is called a double coset

The partition of G into double cosets relative to H and K is a classification, i.e. each gi ∈ G belongs to exactly one double coset. It is also a generalization of the coset decomposition, because the double coset Hg1K contains complete left cosets of K and complete right cosets of H.