\documentclass{article}        % Your input file must contain these two lines 
\usepackage{amsfonts}

\begin{document}               % plus the \end{document} command at the end.

\[ 
\{ x_i \} \subset s \Rightarrow
\exists \  x_0 \in s \  {\textstyle such \  that} \  d(x_i,x_0)
\rightarrow 0 \]





\end{document}                 % The input file ends with this command.