RE: Kevin's excellent question = Is there anyone out there who feels
that "before" and
"after" can permit full ellipsis of the predicate as in the following
example?

(1) My sister arrived at the movie theater before I [arrived at the
theater].

My question, and the one I would ask my students, is, "Why would you
want such a construction? For what purpose?" Is anything really 'saved'
by not simply finishing the construction with "did"? = My sister arrived
at the movie theater before I did.

Just my two cents. Gordon