There is nonempty subset P of R,called the set of positive real number, that satisfies the following
(i) if a,b belong to P, then a+b belongs to P
(ii) if a,b belong to P, then ab belongs to P
(iii)if a belongs to R, Then exactly one of the following hold
aЄP, a=b, -aЄP
The set {-a:aЄP} of negative real number
if aЄP , a>0 a is positive ( a strictly positive )
if aЄPU{0}, a≥0, a is nonnegative real number
if -aЄP, a<0, a is negative ( a strictly negative )
if -aЄPU{0}, a≤, a is nonpositive real number
