module changing_possesion
  depends on entity_event_and_action

  sort declarations
    transfer :: actions
    deliver :: transfer
    lose :: transfer
    receive :: transfer

  function declarations
    fluents
      basic
        possesses : entity * entity -> booleans
    
  axioms
    false if instance(X, transfer),
             -defined_object(X).

    false if instance(X, transfer),
             donor(X, D),
             -instance(D, tangible_entity).

    false if instance(X, transfer),
             recipient(X, Y),
             donor(X, Y).

    occurs(X) causes -possesses(D, O) if instance(X, transfer),
                                         donor(X, D),
                                         object(X, O).

    occurs(X) causes -possesses(R, O) if instance(X, transfer),
                                         recipient(X, R),
                                         object(X, O).
     
    impossible occurs(X) if instance(X, transfer),
                            donor(X, D),
                            object(X, O),
                            -possesses(D, O).


    false if instance(X, deliver),
             -defined_recipient(X).

    false if instance(X, deliver),
             recipient(X, R),
             -instance(R, tangible_entity).

    false if instance(X, deliver),
             donor(X, Y),
             agent(X, Y).

    false if instance(X, deliver),
             recipient(X, Y),
             agent(X, Y).


    false if instance(X, lose),
             -defined_donor(X).

    false if instance(X, lose),
             donor(X, D),
             -instance(D, tangible_entity).


    false if instance(X, receive),
             -defined_recipient(X).