Let A ={1-1/n | n is a natural number}
Prove that 0 is a lower bound and 1 is an upper
bound: Start by taking x in A. Then x = 1-1/n
for some natural number n. Starting from the fact that 0 <
1/n < 1 do some algebra and arithmetic to get to 0 < 1-1/n
<1.
Prove that lub(A) = 1: Suppose that
r is another upper bound. Then wts that r<= 1.
Suppose not. Then r<1. So 1-r>0. Use Archimedes
to show that there is a natural number n such that 1/n<
1-r. Use this to see that r<1-1/n. Thus...
Prove that glb(A) = 0: Suppose that s is
another lower bound. Then wts that 0 <=s. This is
easy to show because 0 is an element of A.
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