dlv [build DEV/Nov  7 2000   gcc egcs-2.91.57 19980901 (egcs-1.1 release)]

{time(1), action(a), action(b), fluent(f), fluent(p), fluent(ff), fluent(pp),
initially(ff), opp(f,ff), opp(p,pp), opp(ff,f), opp(pp,p),
holds(ff,1), occurs(a,1), not_occurs(b,1), holds(p,1), holds(pp,1),
holds(ff,2), holds(f,2), holds(p,2), holds(pp,2), goal_sat, holds(f,1)}