module ext_letting_fall_and_adding_support
  depends on letting_fall_and_adding_support

  function declarations
    fluents 
      basic
        is_at : entity * spatial_entity -> booleans
        is_touching : tangible_entity * tangible_entity -> booleans

  axioms
    is_touching(X, Y) if is_touching(Y, X).
    -is_touching(X, Y) if -is_touching(Y, X).

    impossible occurs(X) if instance(X, let_fall),
                            object(X, O),
                            agent(X, A),
                            -is_at(A, O).

    impossible occurs(X) if instance(X, add_support),
                            object(X, O),
                            agent(X, A),
                            -is_at(A, O).

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