let A and B be bounded nonempty subset of R, and let A+B:={a+b:a element A,b element B}.
prove that the Sup(A+B)=Sup A + Sup B and inf (A+B)= inf A + inf B.
let S subset R be nonempty. show that if u= supremum S, then for every number n element N the number (u-1)/n is not an upper bound of S, but the number (u+1)/n is an upper bound of S.
If f(x)<=g(y) for all x,y element D, then we may conclude that the upremum f(D)<=infimum g(D), which we may write as: Sup f(x)<=inf g(y) such that x,y element of D