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2. EC (1997): Directive 97/68/EC of the European Parliament and of the Council of 16 December 1997
3. EC (2002): Directive 2002/88/EC of the European Parliament and of the Council of 9 December 2002
4. Conley, J; Imagawa, Y.; Kurihara, K.; Rickard, G; Suchdey, S.; Bringhurst, R. (1996): The Optimization of a 26.2 cc, OHV, 4-Cycle Engine Aspiration System to Achieve 1999 CARB Emission Standards, SAE-Paper 961737
5. Dobler, H. (2004): Leichter Viertaktmotor mit Gemischschmierung, MTZ (65) 2004, Nr. 9 Motortechnische Zeitschrift (journal for engine technology), 9/2004, 65th volume