[plt-scheme] syntax-object comparison

Thanks, that does give me some clues.  I'm still trying to wrap my
head around the reasons for the differences, and which ones I need to
use in which situations, but I think I'm starting to figure it out.

It appears that `bound-identifier=?' implies `free-identifier=?'
implies `module-identifier=?'.  The hierarchy seems to be:

  `free-identifier=?' is like `bound-identifier=?' except it also
  works for variables that have no binding.  (or are bound at the top
  level?)

  `module-identifier=?' is like `free-identifier=?' except it also
  knows about module renaming.

Is this correct?  Or are they not strict subsets of each other?

--dougo at place.org