\begin{proposition}\label{assumetest}
    For all $x$ we have $x = x$.
\end{proposition}
\begin{proof}
    Fix $x$.
    Then $x = x$.
\end{proof}

%\begin{proposition}\label{assumetesttwo}
%    For all $x,y,z$ we have $z = z$.
%\end{proposition}
%\begin{proof}
%    Fix $y$.
%    Fix $x,z$.
%    Then $z = z$.
%\end{proof}