doi:10.1002/(SICI)1520-6610(1997)5:5<377::AID-JCD6>3.0.CO;2-CBCH-codescyclotomic cosetsconstructions X and XXconcatenationoptimal codesWe develop the theory of a generalization of the notion ofBCH-code to additive codes, which are not necessarily linear. The usefulness of this notion is ...