Definition 26.5.5. An affine scheme is a locally ringed space isomorphic as a locally ringed space to $\mathop{\mathrm{Spec}}(R)$ for some ring $R$. A morphism of affine schemes is a morphism in the category of locally ringed spaces.

In your comment you can use Markdown and LaTeX style mathematics (enclose it like $\pi$). A preview option is available if you wish to see how it works out (just click on the eye in the toolbar).