PROF=0 will be true if the element is present and equal to zero.
PROF!=0 will be true if the element is present and not equal to zero.
You probably want not(PROF=0) which is true if the element is not present or not equal to zero.
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference