1. EC Directive Dir. 88/76/EEC, December 1987. See also Directives Dir. 88/436/EEC, 16 June 1988, and Dir. 89/458/EEC, 18 July 1989.
2. EC Communication COM (89) 662, 2nd February 1990.
3. ?Vehicle Exhaust Gas Systems,? Harrison, P.G. and Harris, P.J., U.S. Patent 4, 908, 192, 1989.