module letting_fall_and_adding_support
  depends on unobstructing_and_obstructing

  sort declarations
    let_fall :: unobstruct
    add_support :: obstruct

    dive :: let_fall

  function declarations
    fluents 
      basic
        is_supported : tangible_entity -> booleans
        supported_with : tangible_entity * tangible_entity -> booleans

  axioms
    is_supported(O) if supported_with(O, I).
    -supported_with(O, I) if -is_supported(O).

    is_obstructed(X) if is_supported(X).
    -is_obstructed(X) if -is_supported(X).


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

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

    false if instance(X, let_fall),
             agent(X, A),
             -instance(A, tangible_entity).

    false if instance(X, add_support),
             object(X, O),
             -instance(O, tangible_entity).
 
    false if instance(X, add_support),
             instrument(X, I),
             -instance(I, tangible_entity).

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

    false if instance(X, dive),
             agent(X, A),
             -instance(A, animal).

    object(X, A) if instance(X, dive),
                    agent(X, A).


    occurs(X) causes -is_supported(O) if instance(X, let_fall),
                                         object(X, O).

    occurs(X) causes is_supported(O) if instance(X, add_support),
                                        object(X, O),
                                        -defined_instrument(X).

    occurs(X) causes supported_with(O, I) if instance(X, add_support),
                                             object(X, O),
                                             instrument(X, I).

    impossible occurs(X) if instance(X, let_fall),
                            object(X, O),
                            -is_supported(O).

    impossible occurs(X) if instance(X, add_support),
                            object(X, O),
                            instrument(X, I),
                            supported_with(O, I).