  In 1980, Onishchik introduced the index of a Riemannian symmetric space as
the minimal codimension of a (proper) totally geodesic submanifold. He
calculated the index for symmetric spaces of rank less than or equal to 2, but
for higher rank it was unclear how to tackle the problem. In earlier papers we
developed several approaches to this problem, which allowed us to calculate the
index for many symmetric spaces. Our systematic approach led to a conjecture
for how to calculate the index. The purpose of this paper is to verify the
conjecture.
