sig
type t_env = unit
val button_one_press_on_graph : 'a -> unit
val button_two_press_on_graph : 'a -> unit
val button_three_press_on_graph : 'a -> unit
val button_one_press_on_node : 'a -> ViewGraph.t_node -> unit
val button_two_press_on_node : 'a -> ViewGraph.t_node -> unit
val button_three_press_on_node : 'a -> ViewGraph.t_node -> unit
val enter_node : 'a -> ViewGraph.t_node -> unit
val leave_node : 'a -> ViewGraph.t_node -> unit
end