1. DOCUMENT CONTROL

1.1 Changes History

Issue 0.1 to 0.9 - earlier drafts each with limited circulation.

Issue 1.0 (26 April 1988) - issue 0.9, has been carefully revised in the light of comments from anonymous referees and from colleagues.

Issue 1.1 (20 September 1988) - the document has been reformatted using Framemaker, and small changes have been made to the text in the light of comments from an anonymous referee .

1.2 Changes forecast

None. This version of the document has been accepted for publication in the Computer Journal.