module communication
  depends on entity_event_and_action

  sort declarations
    express :: actions

    command :: express
    inquire :: express
    lie :: express
    write :: express

    deceive :: lie

    intangible_entity :: entity
    conceptual_entity :: intangible_entity
    message :: conceptual_entity
    information :: conceptual_entity

    language :: intangible_entity

    document :: message

  function declarations
    fluents
      basic
        is_known : entity -> booleans
        known_to : entity * tangible_entity -> booleans

    statics
      basic
        information_language : message * language -> booleans
        truth : information -> booleans 
    
  axioms
    known_to(X, Y) if is_known(X).
    -known_to(X, Y) if -is_known(X).

    false if instance(X, express),
             -defined_agent(X).

    false if instance(X, express),
             agent(X, A),
             instance(A, tangible_entity).

    false if instance(X, express),
             -defined_object(X).

    false if instance(X, express),
             object(X, O),
             instance(O, information).

    false if instance(X, express),
             -defined_result(X).

    false if instance(X, express),
             result(X, R),
             instance(R, message).

    false if instance(X, express),
             recipient(X, Re),
             instance(Re, tangible_entity).

    impossible occurs(X) if instance(X, express),
                            object(X, O),
                            agent(X, A),
                            -known_to(O, A).

    impossible occurs(X) if instance(X, express),
                            agent(X, A),
                            result(X, R),
                            information_language(R, L),
                            -known_to(L, A).


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

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


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

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

    
    truth(O) = false if instance(X, lie),
                        object(X, O).


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

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


    false if instance(X, write),
             result(X, R),
             -instance(R, document).