%Conformant planning.
% a causes f if p; a causes f if ~p; b causes ~f.
% initially ~f; goal f. plan should be: a.
% goal f


time(1).

action(a).
action(b).

fluent(f).
fluent(p).
fluent(ff).
fluent(pp).

initially(ff).

holds(F,1) :- fluent(F),	initially(F).

opp(f,ff).
opp(ff,f).
opp(p,pp).
opp(pp,p).

holds(F, TT)	:- 	fluent(F),
			fluent(FF),
			opp(F,FF),
			time(T),
			TT = T + 1,
			holds(F,T), 
			not holds(FF, TT).

holds(f, TT)	:-	time(T),
			occurs(a,T),
			TT = T + 1,
			holds(p,T).

holds(f, TT)   :-      time(T),
			TT = T +1,
                        occurs(a,T),
                        holds(pp,T).

holds(ff, TT)  :-	time(T),
			TT = T + 1,
			occurs(b,T).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%occurs(a,1) | not_occurs(a,1).

%occurs(b,1) | not_occurs(b,1).

%	:-	occurs(a,1),
%		occurs(b,1).

not_occurs(A,T)	:- action(A),	
		   time(T),
		   action(B),
		   A != B,
		   occurs(B,T).

occurs(A,T)	:- action(A),
		   time(T),
		   not not_occurs(A,T).

holds(p,1) | holds(pp, 1).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

goal_sat :-	holds(f,2).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

holds(f,1)	:-	goal_sat.
holds(ff,1) 	:-      goal_sat.
holds(p,1)      :-      goal_sat.
holds(pp,1) 	:-      goal_sat.

holds(f,2)      :-      goal_sat.
holds(ff,2) 	:-      goal_sat.
holds(p,2)      :-      goal_sat.
holds(pp,2) 	:-      goal_sat.

:- not goal_sat.