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Something of this form has already been answered here:

Why is $\text{Hom}(V,W)$ the same thing as $V^* \otimes W$?

I'm starting introductory category theory stuff, and I'm looking for some help.

I know that $W\otimes V^{\ast}$ and $\text{Hom}(V,W)$ are naturally isomorphic in the finite dimensional case using the isomorphism $v^{\ast}\otimes w(x)\mapsto v(x)w$. My question is constructing the isomorphism in the other direction, namely $\text{Hom}(V,W)\to W\otimes V^{\ast}$. I'm curious if this can be done without using:

1) Bases, so in particular it should be a natural transformation of finite dimensional spaces, using finiteness only to prove that the given map is indeed an isomorphism.

2) Hom-tensor adjointness. I have read this online and in Rotman, and see how it gives a natural isomorphism for these using a series of equivalences like $\text{Hom}(V\otimes W, U)\to \text{Hom}(V,\text{Hom}(W,U))$.

The basic idea is to say we want a natural transformation $\tau:\text{Hom}(V,-)\to -\otimes V^{\ast}$, so define $\tau_W:\text{Hom}(V,W)\to W\otimes V^{\ast}$ and define $\tau_W(f)=$. It's this latter part I'm having trouble with.

Any help would be greatly appreciated.

amWhy
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Moya
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    Use the inverse if the transformation you already have...? – Pedro Feb 23 '15 at 09:48
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    Pretty sure you have to use bases. Otherwise, you're taking a random $\phi:V \rightarrow W$, and then with nothing but $\phi$ somehow constructing elements of $W$ and elements of $V^*$. It's not possible. If you could do it, then the isomorphism would be true even in the infinite dimensional case. Note that choosing a basis does not break "naturality," because no matter what basis you choose, you'll get the same map. – Cass Feb 23 '15 at 10:03
  • Thanks for the help, I figured out using the previous suggestion of proving basis independence. – Moya Feb 23 '15 at 22:21
  • Checkout this answer to a related question on why basis cannot be avoided https://math.stackexchange.com/a/2463265/296484. – Falcon Mar 03 '20 at 16:30

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