Given a Lie algebra L, return a Cartan subalgebra of L. The algorithm works for Lie algebras L defined over a field F such that |F| > dim L and for restricted Lie algebras of characteristic p. If the Lie algebra does not fit into one of these classes then the correctness of the output is not guaranteed.

> L := SimpleLieAlgebra("F", 4, RationalField());
> L;
Lie Algebra of dimension 52 with base ring Rational Field
> H := CartanSubalgebra(L);
Lie Algebra of dimension 4 with base ring Rational Field
> H*H;
Lie Algebra of dimension 0 with base ring Rational Field
> Normalizer(L, H);
Lie Algebra of dimension 4 with base ring Rational Field