module unrestraining_and_restraining
  depends on unobstructing_and_obstructing

  sort declarations
    unrestrain :: unobstruct
    restrain :: obstruct

  function declarations
    fluents 
      basic
        is_restrained : tangible_entity -> booleans
        restrained_by : tangible_entity * entity -> booleans

  axioms
    is_restrained(O) if restrained_by(O, A).
    -restrained_by(O, A) if -is_restrained(O).

    is_obstructed(X) if is_restrained(X).
    -is_obstructed(X) if -is_restrained(X).


    false if instance(X, unrestrain),
             object(X, O),
             -instance(X, tangible_entity). 

    false if instance(X, restrain),
             object(X, O),
             -instance(X, tangible_entity). 


    occurs(X) causes -is_restrained(O) if instance(X, unrestrain),
                                          object(X, O),
                                          -defined_agent(X).

    occurs(X) causes -restrained_by(O, A) if instance(X, unrestrain),
                                             object(X, O),
                                             agent(X, A).                                         

    occurs(X) causes is_restrained(O) if instance(X, restrain),
                                         object(X, O),
                                         -defined_agent(X). 

    occurs(X) causes restrained_by(O, A) if instance(X, restrain),
                                            object(X, O),
                                            agent(X, A).   


    impossible occurs(X) if instance(X, unrestrain),
                            object(X, O),
                           -defined_agent(X),
                           -is_restrained(O).

    impossible occurs(X) if instance(X, unrestrain),
                            object(X, O),
                            agent(X, A),
                           -restrained_by(O, A).

    impossible occurs(X) if instance(X, restrain),
                            object(X, O),
                           -defined_agent(X),
                           -is_restrained(O).

    impossible occurs(X) if instance(X, restrain),
                            object(X, O),
                            agent(X, A),
                            restrained_by(O, A).