Section Header
    + name := LIMIT_Y;
    - comment := "Sub structure for AREA.";
    - author := "Benoit Sonntag (bsonntag@loria.fr), Jerome Boutet (boutet@loria.fr)";
    - version := 1;
Section Inherit
    - parent_object:OBJECT :=
Section Public
    + value:INTEGER;
    + plan:PLAN;
    + is_top:BOOLEAN;
    + next:LIMIT_Y;
    + prev:LIMIT_Y;
Section Public
    - make y:INTEGER plan p:PLAN is_top b:BOOLEAN <-
    - create_top y:INTEGER plan p:PLAN :LIMIT_Y <-
    - create_bottom y:INTEGER plan p:PLAN :LIMIT_Y <-
    - append old_root:LIMIT_Y :LIMIT_Y <-
    - remove old_root:LIMIT_Y :LIMIT_Y <-
    - set_value v:INTEGER <-
    - set_next new:LIMIT_Y <-
    - set_prev new:LIMIT_Y <-