Supremum is the least upper bound

In summary, the conversation was about proving that the supremum is the least upper bound. The proof presented states that if x is an upper bound of a set S, then x is greater than or equal to the supremum of S. It also states that if there exists an upper bound y that is less than or equal to the supremum, then y is not an upper bound, leading to a contradiction. Therefore, the supremum is always greater than any other upper bound and is therefore the least upper bound.
  • #1
sara_87
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Homework Statement



Prove that the supremum is the least upper bound

Homework Equations





The Attempt at a Solution



Proof: let x be an upper bound of a set S then x>=supS (by definition). If there exists an upper bound y and y<=SupS then y is not an upper bound (contradiction) therefore every upper bound is greater than SupS so SupS is the least upper bound.

Is that proof correct?

Thank you.
 
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  • #2
Please tell what your definitions of "supremum" and "least upper bound" are! As far as I know "supremum" is just another name for "least upper bound" and there is nothing to prove.
 

FAQ: Supremum is the least upper bound

1. What is the definition of "supremum is the least upper bound"?

The supremum of a set is the smallest number that is greater than or equal to all of the elements in the set. It is also referred to as the least upper bound.

2. How is the supremum different from the maximum?

The supremum is the smallest number that is greater than or equal to all of the elements in a set, while the maximum is the largest element in the set. The supremum may or may not be an actual element in the set, whereas the maximum will always be an element in the set.

3. Can the supremum be equal to infinity?

Yes, the supremum can be equal to infinity if the set has no upper bound. In this case, the supremum is considered to be the limit of the set as it approaches infinity.

4. How is the concept of supremum used in mathematics?

The concept of supremum is used in various mathematical fields, such as calculus, real analysis, and topology. It is used to define important concepts like continuity, convergence, and compactness.

5. What is an example of finding the supremum of a set?

An example of finding the supremum of a set is finding the supremum of the set of real numbers less than 1. In this case, the supremum would be 1, as it is the smallest number that is greater than or equal to all the elements in the set.

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