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## How do you prove a supremum exists?

An upper bound b of a set S ⊆ R is the supremum of S if and only if for any ϵ > 0 there exists s ∈ S such that b − ϵ.

## How do you prove that infimum exists?

Similarly, given a bounded set S ⊂ R, a number b is called an infimum or greatest lower bound for S if the following hold: (i) b is a lower bound for S, and (ii) if c is a lower bound for S, then c ≤ b. If b is a supremum for S, we write that b = sup S. If it is an infimum, we write that b = inf S.

Is supremum the same as maximum?

In terms of sets, the maximum is the largest member of the set, while the supremum is the smallest upper bound of the set.

### What is supremum of a function?

The supremum (abbreviated sup; plural suprema) of a subset of a partially ordered set is the least element in that is greater than or equal to all elements of if such an element exists. Consequently, the supremum is also referred to as the least upper bound (or LUB).

### Can a bounded set not have a supremum?

The set {x∈Q∣x2<2} does not have a supremum in Q, even though it is bounded. However, it does have a supremum if we view it as a subset of R. This is an example of how the least upper bound property (every set bounded from above has a supremum) encodes completeness.

What is the difference between supremum and upper bound?

A set is bounded if it is bounded both from above and below. The supremum of a set is its least upper bound and the infimum is its greatest upper bound. If M ∈ R is an upper bound of A such that M ≤ M′ for every upper bound M′ of A, then M is called the supremum of A, denoted M = sup A.

#### Is the number 0 a real number?

Real numbers are, in fact, pretty much any number that you can think of. This can include whole numbers or integers, fractions, rational numbers and irrational numbers. Real numbers can be positive or negative, and include the number zero.

#### What is the supremum of R?

The supremum of a set is its least upper bound and the infimum is its greatest upper bound. Definition 2.2. Suppose that A ⊂ R is a set of real numbers. If M ∈ R is an upper bound of A such that M ≤ M′ for every upper bound M′ of A, then M is called the supremum of A, denoted M = sup A.

How do you prove something is the least upper bound?

It is possible to prove the least-upper-bound property using the assumption that every Cauchy sequence of real numbers converges. Let S be a nonempty set of real numbers. If S has exactly one element, then its only element is a least upper bound.

## How to prove the supremum and inﬁmum proof?

The supremum and inﬁmum Proof. Suppose that M, M′ are suprema of A. Then M ≤ M′ since M′ is an upper bound of A and M is a least upper bound; similarly, M′ ≤ M, so M = M′. If m, m′ are inﬁma of A, then m ≥ m′ since m′ is a lower bound of A and m is a greatest lower bound; similarly, m′ ≥ m, so m = m′.

## How to prove supremum and infimum in Stack Exchange?

Here the supremum case: For any positive integers m, n with m < n, then m / n < 1, so we get immediately sup X ≤ 1. Now we claim that sup X = 1.

Can a set bigger than 2 be a supremum?

Assume that M is the supremum and M < 2. Of course, M > 2 is trivially impossible since 2 is an upper bound as well and thus any M bigger than 2 cannot be a supremum. Now, let x = 2 − M 2 + M.

### Is there suprema and inﬁma in r.theorem 2.6?

In fact, the existence of suprema and inﬁma is one way to deﬁne the completeness of R. Theorem 2.6. Every nonempty set of real numbers that is bounded from above has a supremum, and every nonempty set of real numbers that is bounded from below has an inﬁmum.