Let $K$ be a field (not necessarily algraically closed). Let $\mathcal{F}$ be a contravariant functor from the category of schemes over $K$ to sets and $M$ be a coase moduli space for the functor. So, there is a morphism of contravariant functors from $\mathcal{F}$ to $h_M$ where $h_M:=Hom(−,M)$ such that $\mathcal{F}(\bar{K})$ is bijective to $h_M(\bar{K})$, where $\bar{K}$ is an algebraic closure of $K$. So, the natural morphism from $\mbox{Spec}(\bar{K})$ to $\mbox{Spec}(K)$ gives rise to a natural transformation. As far as I understand this means that if $\mathcal{F}(K)$ is nonempty which maps to something nonempty in $\mathcal{F}(\bar{K})$ the image of $\mathcal{F}(K)$ in $h _M(\bar{K})$ under the composition of the morphism $\mathcal{F}(K) \to \mathcal{F}(\bar{K}) \xrightarrow{\sim} h_M(\bar{K})$ is nonempty (due to the bijectivity over $\bar{K}$). By the commutativity of the diagram (coming from the natural transformation) this means that $h_M(K)$ is nonempty. Is this correct?
Take the 2minute tour
×
MathOverflow is a question and answer site for professional mathematicians. It's 100% free, no registration required.
closed as offtopic by Neil Strickland, Daniel Loughran, Steven Sam, Stefan Kohl, abx Jun 8 '14 at 21:23


