Central ideal

A central ideal $𝔞 ⊴ 𝔷 (𝔤) ⊴ 𝔤$ of a Lie algebra $𝔤$ is a linear subspace of its centre $C e n t 𝔤$ . lie Any such subspace is necessarily an ideal, since $[𝔞, 𝔤] = {0}$ .