  For a given abelian group G, we classify the isomorphism classes of
G-gradings on the simple Lie algebras of types A_n (n >= 1), B_n (n >= 2), C_n
(n >= 3) and D_n (n > 4), in terms of numerical and group-theoretical
invariants. The ground field is assumed to be algebraically closed of
characteristic different from 2.
