4%% Include the BASIC EVENT CALCULUS THEORY
    5#include '../bec_theory'.

    9% If a light is turned on, it will be on:
   10initiates(turn_on, light_on, T).
   11
   12% If a light is turned on, whether it is red or green will be released
   13% from the commonsense law of inertia:
   14releases(turn_on, light_red, T).
   15releases(turn_on, light_green, T).
   16
   17% If a light is turned off, it will not be on.
   18terminates(turn_off, light_on, T).
   19
   20% After a light is turned on, it will emit red for up to two seconds
   21% and green after at least two seconds:
   22trajectory(light_on, T1, light_red, T2) :- T2 .>=. T1, T2.<.T1 + 2.
   23trajectory(light_on, T1, light_green, T2) :- T2 .>=. T1 + 2.
   24
   25initiallyN(light_on).

   28happens(turn_on, 1/2).
   29happens(turn_off, 4).
   30happens(turn_on, 6).

   39% ?- holdsAt(light_on, -1).                           % no
   40 ?- holdsAt(light_on, 2).                            % success  
   41% ?- holdsAt(light_on, 4).                            % success 
   42% ?- holdsAt(light_on, 5).                            % no      
   43% ?- holdsAt(light_on, 6).                            % no      
   44% ?- holdsAt(light_on, 104/10).                       % success
   45                                     
   46% ?- -holdsAt(light_on, 1/10).                        % no
   47% ?- -holdsAt(light_on, 2).                           % no      
   48% ?- -holdsAt(light_on, 5).                           % success
   49                                     
   50% ?- T is 1/2 + 2 - 1/10, holdsAt(light_red, T).      % success
   51% ?- T is 1/2 + 2 + 1/10, holdsAt(light_red, T).      % no
   52% ?- holdsAt(light_red, 4).                           % no      
   53% ?- holdsAt(light_red, 6).                           % success 
   54% ?- holdsAt(light_red, 8).                           % no      
   55% ?- holdsAt(light_green, 6).                         % no      
   56% ?- holdsAt(light_green, 8).                         % success