I have not seen this white paper myself but most likely it originated from our online help documentation specific to the Net Properties/CES formula examples.
If you go into the install directory and look for 2007EE\SDD_HOME\common\help\pcb\netpropsdlg.chm, then double click on this .chm file and open the index to Delay Formula -> Examples you will find some very good information on formula syntax and entry examples. There are also some examples under Defining Delay Formulas and Common Shorthand Syntax.
Also, this documentation exists within the CES online help system at: <Install>\2007EE\docs\htmldocs\ces_user\wwhelp\wwhimpl\js\html\wwhelp.htm
The CES documentation has some good information on using Free Variables within the system as part of a formula definition. Use the index and search for Free in order to find the page on "Using Free Variables to Constrain Delay by Group Only:.
Product Marketing Manager Expedition / Xtreme PCB