Central ideal
= Central ideal
A central ideal is a <linear subspace> of the <center of a Lie algebra>. It is a <Lie algebra ideal> because its <Lie bracket> with every element is zero. Passing to the <quotient Lie algebra> removes this central subspace. For $\mathfrak{sl}_p$ in <characteristic> $p$, the identity matrix has zero <trace> and spans a central ideal.