prompter: Let E be a normed space and F a Banach space. Prove that the set of bounded linear operators from E to F (which you can assume to already be a vector space with respect to suitable operations and field), equiped with the operator norm, is also a Banach space.
assistant: Let's denote the set of bounded linear operators from E to F by B(E,F). We need to show that B(E,F) is complete with respect to the operator norm. Let (Tn) be a Cauchy sequence in B(E,F). Then for any ε > 0, there exists N such that for all n,m ≥ N, we have ||Tn - Tm|| < ε. 

Now let x ∈ E be arbitrary and fixed. Then we have ||Tnx - Tmx|| ≤ ||Tn - Tm|| ||x|| < ε ||x||. This shows that (Tnx) is a Cauchy sequence in F. Since F is a Banach space, it follows that (Tnx) converges to some element Tx ∈ F.

We claim that the map T: E → F defined by Tx = lim(Tnx) is a bounded linear operator and that Tn → T in the operator norm.

Linearity of T follows from linearity of each Tn and the fact that limits preserve linear operations. To see that T is bounded, note that for any n ≥ N and any x ∈ E we have ||Tx|| = lim(||Tnx||) ≤ lim(||Tn - TN|| ||x|| + ||TNx||) ≤ ε ||x|| + ||TNx||. Taking supremum over all x with ||x|| = 1 shows that ||T|| ≤ ε + ||TN|| < ∞.

Finally, let's show that Tn → T in the operator norm. For any n ≥ N and any x ∈ E we have
    | | |Tx - Tnx| | |
    = | | |lim(Tmx) - Tnx| | |
    ≤ lim(| | |Tmx - Tnx| | |
    ≤ lim(| | |(Tm-Tn)x| | |
    ≤ lim(| |(Tm-Tn)| *|x|)
    = 0

This shows that for any n ≥ N we have
    max{0 <= k <= n} (| |(Tk-T)|| ) 
    <= max{0 <= k <= N} (| |(Tk-T)|| ) + ε

Since this holds for all ε > 0 it follows that Tk → T in the operator norm as k → ∞.

Thus we have shown that every Cauchy sequence in B(E,F) converges to an element of B(E,F), so B(E,F) is complete with respect to the operator norm and hence a Banach space.
prompter: Can you explain this in layman's terms?
assistant: Certainly! I'll try to provide a simpler explanation without delving too deep into the technical details.

In the world of mathematics, we have something called a "space," which is a collection of elements with certain properties. A Banach space is a special kind of space that has an additional property: every "Cauchy sequence" of elements in the space has a limit within the space itself. A Cauchy sequence is a sequence of elements that get closer and closer to each other as you go further along in the sequence.

Now, we have two spaces, E and F, where F is already known to be a Banach space. We want to look at a special kind of transformation called "bounded linear operators" that can turn elements from space E into elements in space F.

The main goal of the problem is to show that the set of all these transformations (bounded linear operators), when equipped with a specific way of measuring the "size" of transformations called the "operator norm," is also a Banach space.

The proof involves showing that every Cauchy sequence of transformations converges to a limit within the set of transformations. To do this, we first examine what happens to a single element from space E when it goes through the transformations in the Cauchy sequence. We find that the transformed elements form a Cauchy sequence in space F, and since F is a Banach space, this sequence must have a limit within F.

Then, we show that there is a transformation that turns each element from E into the limit of the transformed elements in F. This transformation is also a bounded linear operator, and we show that the Cauchy sequence of transformations converges to this new transformation.

Thus, we have proven that the set of bounded linear operators, equipped with the operator norm, is also a Banach space. This means that this set of transformations has the same "completeness" property as the Banach space F, which is an important result in the study of functional analysis.