> **Possible Duplicate:**  
> [Is it true that, as Z-modules, the polynomial ring and the power series ring over integers are dual to each other?](https://mathoverflow.net/questions/10239/is-it-true-that-as-z-modules-the-polynomial-ring-and-the-power-series-ring-over)  


Is there an easy proof? I only found citations but have no access. By the way: If we cross over to the rationals every vector space is free (using Zorn's lemma). But can one construct a basis of "Countable infinite product of the rationals"?