Background/motivation
It is a classical fact that we have a natural isomorphism Symn(V∗)congSymn(V)ast for vector spaces V over a field k of characteristic 0. One way to see this is the following.
On the one hand elements of Symn(V∗) are symmetric powers of degree n of linear forms on V, so they can be identified with homogeneous polynomials of degree n on V. On the other hand elements of Symn(V)ast are linear functionals on SymnV; by the universal property of SymnV these correspond to n-multilinear symmetric forms on V. The isomorphism is then as follows.
An n-multilinear symmetric form phi corresponds to the homogeneous polynomial p(v)=phi(v,dots,v). In the other direction to a polynomial p(v) we attach the multinear form obtained by polarization phi(v1,dots,vn)=frac1n!sumIsubset[n](−1)n−sharpIp(sumiinIvi). Here [n] is the set lbrace1,dots,nrbrace.
Problem
Of course this will not work for n greater than the characteristic of k if the latter is positive.
One can expect that an isomorphism Symn(V∗)congSymn(V)ast holds also in positive characteristic, and that this should be trivially true by using the universal properties of the symmetric powers. The problem is that if I try to define a natural map between the two spaces using the universal properties I have at some point to divide by n! anyway.
Still there may be some natural isomorphism that I cannot see. Or maybe there is not a natural isomorphism, but I don't know how to prove this.
Is there a natural isomoprhism Symn(V∗)congSymn(V)ast in positive characteristic?
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