@incollection{Halliday94-theory,
  author	= {Halliday, M. A. K.},
  editor	= {Asher, R. E.},
  year		= {1994},
  title		= {Systemic theory},
  booktitle	= {The encyclopedia of language and linguistics},
  publisher	= {Pergamon Press},
  address	= {Oxford}
}