The email newsletter Impressions May 2009 issue arrived here yesterday. It is a publicity email from International Tyepface Corporation of which http://www.itc.com is the webspace.
The newsletter has a link to an article about standard ligatures.
http://www.itcfonts.com/Ulc/4112/StandardLigatures.htm
The article has the following appended.
(Stay tuned for Part II, on Discretionary Ligatures)
William Overington
13 May 2009