\begin{verbatim}


%%
%% block2-2-1.sm
%%
%% This program tests if the encoding for appx planning is
%% correct or not.

 const length=2.
 time(1..length).

 initially(neg(f)).

 fluent(f).
 fluent(p).

 action(a).
 action(b).

 executable(A,T)    :-
                action(A),
                time(T).

 causes(a, f, s5).

 in(p, s5).

 causes(b, p, s6).

 set(s5).

 set(s6).

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

goal(T)     :-
            time(T),
            not holds(f,T),
            not holds(neg(f), T).

% We are looking for a plan that makes f unknown.

exists_plan :-
        goal(length).

:- not exists_plan.


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


literal(G)  :-
    fluent(G).

literal(neg(G)) :-
    fluent(G).

contrary(F, neg(F)) :-
    fluent(F).

contrary(neg(F), F) :-
    fluent(F).


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

not_holds_set(S, T)   :-
    set(S),
    time(T),
    literal(L),
    in(L,S),
    not holds(L,T).

holds_set(S, T)        :-
    set(S),
    time(T),
    not not_holds_set(S,T).

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

m_not_holds_set(S, T)   :-
    set(S),
    time(T),
    literal(L),
    literal(LL),
    in(L,S),
    contrary(L,LL),
    holds(LL,T).

m_holds_set(S, T)        :-
    set(S),
    time(T),
    not m_not_holds_set(S,T).

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

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


holds(F, T+1)   :-
    literal(F),
    time(T),
    set(S),
    T < length,
    action(A),
    executable(A,T),
    occurs(A,T),
    causes(A,F,S),
    holds_set(S,T).

ab(F, T+1)   :-
    literal(F),
    time(T),
    set(S),
    T < length,
    action(A),
    executable(A,T),
    occurs(A,T),
    causes(A,F,S),
    m_holds_set(S,T).


holds(F, T+1)   :-
    literal(F),
    literal(G),
    contrary(F,G),
    time(T),
    T < length,
    holds(F,T),
    not ab(G, T+1).


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

possible(A,T)   :-
    action(A),
    time(T),
    executable(A,T),
    not goal(T).

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

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

not_occurs(A,T) :-
    action(A),
    action(AA),
    neq(A,AA),
    time(T),
    occurs(AA,T).


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

 hide time(T).
 hide action(A).
 hide causes(A,F,S).
 hide initially(F).
 hide contrary(F,G).
 hide fluent(F).
 hide literal(L).
 hide executable(A,T).
 hide holds(F,T).
 hide not_occurs(A,T).
 hide possible(A,T).
% hide possible1(A,T).
% hide possible2(A,T).
% hide block(X).
 hide exists_plan.
 hide finally(X).
 hide goal(T).
% hide not_goal(T).
 hide set(S).
 hide in(X,Y).
 hide holds_set(X,Y).
 hide not_holds_set(X,Y).
% hide exec(A,S).
% hide not_executable(A,T).
 hide ab(F,T).
 hide m_not_holds_set(S, T).
 hide m_holds_set(S, T).

\end{verbatim}