\documentclass[a4paper,12pt]{article}

\usepackage[italian]{babel}
\usepackage[utf8x]{inputenc}
%\usepackage[latin1]{inputenc}

\usepackage{amsmath}


\usepackage{amssymb} % carica simboli matematici aggiuntivi 

\begin{document}


Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Ut purus elit, vestibulum ut, placerat ac, 
\begin{displaymath}
	f_{n} \rightarrow f
\end{displaymath}
adipiscing vitae, felis. Curabitur dictum gravida mauris.


Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Ut purus elit, vestibulum ut, placerat ac, 
\begin{displaymath}
	50 \vdash 55
\end{displaymath}
adipiscing vitae, felis. Curabitur dictum gravida mauris.




\end{document}