Could some one point me in the right direction with this proof to get me started? I'm not sure where to begin.
If a set A ⊆ R contains one of its upper bounds s, prove that s is the supremum of A.
An upper bound: If a set A⊆R a real number s is an upper bound for A if for all x A, x s.
a supremum: a real number s is least upper bound for A if s is an upper bound for A having the property that, if b is also an upper bound for A then s b.
So am I showing that there is a y such that y>s- or is that still just the definition. I'm sorry I think it is the wording of the question that is throwing me off.