\nocaret\normalsize\pagecolor{silver}%
%\def\gal#1#2{{{\rm Gal}({#1} / {#2})}}
%\def\nese{\begin{array}{c}\nearrow\sim \\ \searrow\sim \end{array}}
\def\piArith{{\pi_1^{\rm arith}}}
\def\rightisom{\stackrel{\sim}{\rightarrow}}
\def\sep#1{{{#1}^{\rm sep}}}
\def\Spec#1{{{\rm Spec}\,({#1})}}
\def\tensor#1{\mathop{\otimes}_{#1}}
\def\xbar{{\overline{x}}}
\def\ybar{{\overline{y}}}
$$
\begin{array}{ccccc}
\pi_1(\Spec{L},\ybar) & \rightarrow & \pi_1(E,\ybar)      & \rightisom & \piArith(E) \\
          ||          &             &     \downarrow \pi_*& & \downarrow \pi_* \\
\pi_1(\Spec{L},\xbar) & \rightarrow & \pi_1(U \tensor{k} L,\xbar) &
\rightisom & \colorbox{blue}{\color{white}\piArith(U \tensor{k} L)}
\end{array}