- My last message was wrong. The equation is correct logically it seems. One half of a disjunction would read At(P1, JFK)0 AND NOT (At (P1, JFK)0) which would always be false so the disjunction's truth would depend on the other half which would be At(P1, JFK)0 AND NOT (Fly (P1, SFO, JFK)0 which is correct. However, the equation would have a logically equivalent and more natural reading if the first half of the two-part disjunction on the right-hand side simply read (At(P1, JFK)0 AND NOT Fly(P1, JFK, SFO)0.Some additional errors are 1) page 406 line 16 Leftrightarrow should be replaced by an actual arrow; and 2) page 284 figure 9.5 line 2: add AND symbol between Diff(nt, q) and Diff(nt, sa)Luke Hodgkinson