%
% Nondeterministic theory 
%

% define fluents and actions 

fluent(f).
fluent(g).
fluent(h).


action(a).

% define time line 

time(0..n).

% initial state 

h(neg(f), 0).
h(neg(g), 0). 
h(neg(h), 0).

% action effects 

h(f, T+1):-
    time(T), o(a, T).


% static causal laws 

h(h, T):-
    time(T), h(f, T), h(neg(g), T).

h(g, T):-
    time(T), h(f, T), h(neg(h), T).

% action occurrences 

o(a, 0).

% what was missing is the rule that say "thing do not 
% change by themselve" 

% F was true at T and is not false at T+1 then 
% F must continue to be true at T 

h(F, T+1):- 
    time(T), T<n, fluent(F), 
    h(F, T), not h(neg(F), T+1). 

% F was false at T and is not true at T+1 then 
% F must continue to be false at T 

h(neg(F), T+1):- 
    time(T), T<n, fluent(F), 
    h(neg(F), T), not h(F, T+1). 

% hiding fluent and action 

hide fluent(F).
hide action(A).

% hiding time 

hide time(T).