descend(Term t, int subtermIndex) Determine the cache that is responsible for locations within the
subtermIndex'th subterm of the term t
(assuming that this cache is responsible for the location
of the term t).
Determine the cache that is responsible for locations within the
subtermIndex'th subterm of the term t
(assuming that this cache is responsible for the location
of the term t). This method is used in
TermTacletAppIndex when recursively constructing the index
for a given term.