7. The method of claim 1, wherein each expression is a word, so that in step (a) said computer determines a frequency of occurrence of words in the document.
7. The method of claim 1, wherein each expression is a word, so that in step (a) said computer determines a frequency of occurrence of words in the document. 9. The method of claim 7, further comprising, using said computer, performing a word-stemming operation on words in said document prior to performing step (a).