#const n=3.      

%%%%%%%%%%%%%%%%%%%%  SCENARIO 9  %%%%%%%%%%%%%%%%%%%%
%                                                    %   
%  John is in Boston on Dec 1. He has no passport.   %
%  Can he go to Paris on Dec. 4?                     %
%                                                    %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


% The only difference here is the date of departure.
% This means that the only change is the constant
% in definnition of answer_true.
% This time it is possible for John to go to Paris
% on time (assuming of course that he'll receive
% his passport quickly). Hence the answer to the query 
% should be YES.


%           THE TRANSLATION

% translation of the first two sentences is straightforward.

%  John is in Boston on Dec 1. 

h(at(john,boston),0).
time(0,d,1).

% He has no passport.

-h(has(john,passport(john)),0).

% The query however is rather different from what we've seen
% so far. It can be interpreted as asking if there is a plan
% (a sequence of actions) which will allow John to go to 
% Paris on Dec 3.
% (Recall that to go John needs a passport and that getting
% one requires at least three days. So no such plan exists
% and the answer to our query should be "NO").
% The query can be translated by a rule:

answer_true(q) :-  
     o(go_on(john,j(boston,paris)),T),
     time(T,d,4).

% In general we may have
%
% answer_true(Q) :- h(F,T),...,o(a,T)...
%                   time(T,U,V),...
%
% that is, the query may contain conditions
% regarding several fluents, occurrences of actions,
% and time atoms encoding dates and other time
% measures.

type_query(q,can).   

% The next fact states that the query
% is about JOHN's ability to plan
% his trip to Paris.

planner(q,john).

% To answer this query we need a planning module
% described below:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                            %
%             THE PLANNING MODULE            %
%                                            %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% The module, used in conjunction with "scenario9" 
% and travel takes a non-negative integer n
% as a parameter and finds a plan of maximum 
% length n which achieves the goal. If no
% such plan exists the program has no model.

yes :- 
   type_query(Q,can),   
   answer_true(Q).

:- not yes.

{o(Act,T) : action(Act) : actor(Act,P)}1 :- 
                      planner(Q,P),
                      T < n-1.

hide.
show  yes.

% show time(A,B,C),  do(A,B).


% As before we need our "AboutTime" module:

%%%%%%%%  AboutTime

1{time(T,d,X) : day(X)}1 :- T < n.

:- time(T1,d,Day1),
   time(T2,d,Day2), 
   T1 < T2, 
   Day2 < Day1.

:- time(T,d,Day1),
   time(T,d,Day2),
   neq(Day1,Day2).

% The following actions are performed
% during a single day.

time(T+1,d,Day) :- 
         o(pack(P,PP,Container),T),
         time(T,d,Day).

time(T+1,d,Day) :- 
         o(embark(P,J),T),
         time(T,d,Day).

time(T+1,d,Day) :- 
         o(stop(J,C),T),
         time(T,d,Day).

time(T+1,d,Day) :- 
         o(disembark(P,J),T),
         time(T,d,Day).