## Erratum:

As observed by Frits Vaandrager about a month after
publication, my new term model is *not* isomorphic to the
one of [TCS51]. For divergence-free process the models are
isomorphic, but in general my model makes strictly less
identifications. In particular, contrary to what I claimed,
my model does not satisfy KFAR, whereas the one from
[TCS51] does. It also does not satisfy the weakenings of
KFAR discussed in the paper, but it does satisfy the
weakening KFAR- as proposed in the cited
paper by Bergstra, Klop & Olderog (1986).

The results concerning the relative inconsistency of four widely
used proof-principles are unaffected by this mistake.
The new restriction of AIP is valid in both the new model
and the model of [TCS51].

The easiest repair would be to drop the new model from the
paper and replace it by recalling the model of Baeten,
Bergstra & Klop (1985) [TCS51]. That model is based on
Milner's notion of weak bisimulation semantics, and
additionally distinguishes deadlock from successful
termination.

However, the new model is interesting in its own right,
even when it can not be seen as an alternative presentation
of the one from [TCS51]. In particular, Bol & Groote (1990)
[The meaning of negative premises in transition system
specifications, ICALP'91] define a compositional priority
operator in this model that allows silent actions to have
priority over certain visible actions, which would not be
possible in weak bisimulation semantics as employed in
Milner (1980) or [TCS51].