We are assuming that the predicate 
is ambiguous in the discourse
contexts since it can be ambiguously interpreted as either the predicate
or as the predicate 
in some
knowledge base. In the third question the predicate is disambiguated for
context c6. This will allow us to prove that the GE bid on the FX22 engine is
$4M including spare parts. Note that we will have to state the above in the kb
context because the discourse contexts are not expressive enough to distinguish
between the price including spares and the price excluding spares (which in fact
was the source of ambiguity).
Theorem (kb):
ist(c_kb 
,price-including-spares(engine(22),$4M))
Proof !kb(kb): By reasoning similar to the first question, we can conclude
From the frame axioms we get
similarly to the frame derivation in the second question.
Now the theorem follows from the above formulas.
See [10] for more details.