Let (π,π ,+,β ) be a (left) module.
A submoduleπβ€π is a module under the same operations, module
i.e. (π,+) is a subgroup such that πβ πβπ for any πβπ and πβπ .
Thus a submodule is an invariant subspace under the carried representation of π (see invariant subspace).
Examples
Let πΌβ΄π be an ideal. Then πΌ is an π -submodule of π .