Let $\frak{g}$ be a finite-dimensional nilpotent complex Lie algebra. What is known about the dimensions of the ideals of $\frak{g}$? (For instance, $\frak{g}$ admits an ideal of codimension 1, provided that $\frak{g}$ is non-trivial.) Also, what (if any) results are there concerning the existence of ideals of certain dimensions and the index of $\frak{g}$?
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