In my ignorant youth, I once used em(1), so called Ed for Mortals.  I
can't now remember what the differences were.  Perhaps it printed
'huh?'  rather than '?'  to be more 'helpful'.  Anyhow, I only had to
transpose 'e' to 'r' once when invoking it (easily done, even on
boyd's keyboard) to decide never to use it again.