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%%%%%   A Block World  [Kowalski, page 135]
 
%--------------------------  Infix definition ----------------------------------
% Здесь я попытался дать определения, но что-то совсем потерялся. 
:- op(500, xf, clear).
:- op(500, xfx, on).
:- op(500, xfx, movedFrom).
:- op(500, xfx, to).
:- op(500, xf, movable).
 
% Infix operator definitions.
Object clear :- not(X on Object).
Object movable.
Object movedFrom X :- Object movable, Object on X.
Object to X :- Object movable, X clear.
 
 
 
% State-independent assertions
 
a moveable.
b moveable.
c moveable.
 
% Goal state
 
goal(Done) :- a on b when Done , b on c when Done ,
              c on r    when Done , Done ok , !.
 
% State-space
 
ok(start).            % Initial state
 
X movedFrom Y to Z after Work ok :-
    Work ok ,
    X moveable, X clear when Work ,
    Z clear when Work , X on Y when Work , X \= Z.
 
a on b when start.    % Initial state
b on p when start.    % Initial state
c on r when start.    % Initial state
a clear when start.   % Initial state
q clear when start.   % Initial state
c clear when start.   % Initial state
 
X on Z when X movedFrom _ to Z after _.
 
Y clear when _ movedFrom Y to _ after _.
 
NewState when X movedFrom Y to Z after Work :-
    NewState when Work ,
    NewState \= X on Y ,
    NewState \= Z clear.
 
:- begin_tests(bw).
 
% If you run goal(Done) then you should see the value of Done as written
% in the test.
 
test(goal) :- goal(Done) ,
    Done = a movedFrom q to b
            after (b movedFrom p to c
            after (c movedFrom b to r
            after (c movedFrom r to b
            after (a movedFrom b to q
            after start)))).
 
:- end_tests(bw).