the.com/subgroup

A clique inside a group that still plays by the group's rules.

means A smaller set of elements chosen from a larger group that still satisfies all the structural rules of the original group — closure, identity, and inverses included.

from Built from sub- (Latin for 'under' or 'below') plus group, the mathematical term borrowed from everyday English in the 1800s as algebraists like Galois and his successors formalized 'group' into a precise structure with its own laws of combination — a subgroup is simply a smaller society living under that same constitution.

closure test
must stay inside under the same operation
smallest member
every group contains the trivial one-element subgroup
identity rule
must include the group's identity element
cosets
slice the whole group into equal-sized pieces
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