Most likely this result can be extended to for example
.
De
Jongh uses the fact that
is
in
iff
for all
,
.
Now suppose A is essentially
but not provably
equivalent to some
.
A model of
and
is made. It seemed quite difficult to
extend this method to
.
The author and Rosalie Iemhoff have
payed some effort to do so. With the construction method presented in
this paper it might be possible to reduce the problem to an easier
statement.