I got this error:
INTERNAL ERROR: unbound method is_absolute() must be
called with ImmutableName instance as first argument
(got nothing instead)
when I added the text
"""Raised if an attempt is made to append anything
other than the
empty name to an absolute name."""
to my source. The error is bogus; the class added has
do with the one which has is_absolute. It seems to be
some kind of name collsion. If I rename
'AbsoluteConcatenation' or even
'FAbsoluteConcatenationAttempt', the problem goes away.