> We will need to determine whether source files for runs of various
# programs are out of date. In a normal situation, this is done by
# asking whether the times of the source files are later than the
# destination files. But this won't work for us, since a common
# situation is that a file is written on one run of latex, for
# example, and read back in on the next run (e.g., an .aux file).
# Some situations of this kind are standard in latex generally; others
# occur with particular macro packages or with particular