`  ::We are reviving a discussion that took place at the beginning of the 20th century, but which most modern mathematicians consider settled (see Fraleigh, above), and which goes far beyond the scope of this article.  Selfstudier is correct in noting that there are a few holdouts.  He is also correct in noting that they are a minority.  Note that I do not object to the use of the word ``rule`` in the article.  Rather, I want the common opinion of most modern mathematicians to be included as well, and, since it is the majority opinion, not labled dubious.   `