Judgment of the Court of 20 March 2002 in Case T-9/99, HFB Holding für Fernwärmetechnik Beteiligungsgesellschaft mbH & Co. KG and Others v Commission of the European Communities (Competition — Cartel — District heating pipes — Article 85 of the Treaty (now Article 81 EC) — Boycott — Fine — Guidelines on setting fines — Objection of illegality — Non-retroactivity — Rights of defence — Leniency notice)