  A $G$-grading on a complex semisimple Lie algebra $L$, where $G$ is a finite
abelian group, is called quasi-good if each homogeneous component is
1-dimensional and 0 is not in the support of the grading.
  Analogous to classical root systems, we define a finite root system $R$ to be
some subset of a finite symplectic abelian group satisfying certain axioms.
There always corresponds to $R$ a semisimple Lie algebra $L(R)$ together with a
quasi-good grading on it. Thus one can construct nice basis of $L(R)$ by means
of finite root systems.
  We classify finite maximal abelian subgroups $T$ in $\Aut(L)$ for complex
simple Lie algebras $L$ such that the grading induced by the action of $T$ on
$L$ is quasi-good, and show that the set of roots of $T$ in $L$ is always a
finite root system. There are five series of such finite maximal abelian
subgroups, which occur only if $L$ is a classical simple Lie algebra.

Group Theory;Representation Theory