The Lie algebra L and the subalgebra I can be provided either from their structure constants or their infinitesimal generator representation. When providing the Lie algebra L with its structure constants denote the elements of the subspaces by using the symbol X, e.g. {X[1], X[4]}.
The command checks if the supplied subalgebra I is indeed an ideal of the Lie algebra L.
If the null ideal is given ({}) then the structure constants of the initial Lie algebra will be returned.