Yes, 0 is the ultimate composite number. The use of the phrase "characteristic zero" is merely a hack, and nothing should be read into this usage. Once again, the primary reason for considering these 'corner cases' is to reduce the number of 'special cases' in definitions and proofs. In many cases, a formula can be extended to include the case n=0 or p=1 if the appropriate extended definition is used. It is easy to handle some of these definitions with "for all x in A, E(x)", so long as you realize that this works even when A is the empty set. Unfortunately, many speakers of English assume that when you talk about such an x, you seem to imply that such an x actually exists. At 06:26 AM 2/10/2014, Andy Latto wrote:
Do the people who say that 1 is a prime also say that 0 is a composite?