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Feb 18, 2012 at 18:54 comment added B R But an abelian Lie algebra is reductive!
Feb 18, 2012 at 18:52 comment added anon Even simpler, an abelian Lie algebra is a Cartan subalgebra of itself.
Feb 18, 2012 at 16:46 comment added Salvatore Siciliano BR: Yes, you are right.
Feb 18, 2012 at 16:32 comment added B R This method works whenever $\mathfrak b$ is a subalgebra of a reductive Lie algebra $\mathfrak g$ and $\mathfrak b$ contains a Cartan subalgebra $\mathfrak a$ of $\mathfrak g$ (Since $\mathfrak a$ is its own normalizer in $\mathfrak g$, it will be its own normalizer in $\mathfrak b$).
Feb 18, 2012 at 16:27 comment added Salvatore Siciliano Indeed, the subalgebra of diagonal matrices is also a Cartan subalgebra of $gl_n(F)$ for any field $F$ and $n>0$.
Feb 18, 2012 at 4:59 history answered B R CC BY-SA 3.0