module locomotion
  depends on motion

  sort declarations
    locomotion :: move

    carry :: locomotion
    go_to :: locomotion
    leave :: locomotion
    walk :: locomotion

  function declarations
    fluents 
      basic
        held_by : tangible_entity * tangible_entity -> booleans

  axioms
    false if instance(X, locomotion),
             -defined_agent(X).

    object(X, Y) if instance(X, locomotion),
                    agent(X, Y).

    agent(X, Y) if instance(X, locomotion),
                    object(X, Y).


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

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

    impossible occurs(X) if instance(X, carry),
                            object(X, O),
                            agent(X, A),
                            -held_by(O, A).


     false if instance(X, go_to),
              -defined_destination(X).

     false if instance(X, leave),
              -defined_origin(X).