\documentclass{article}
\usepackage{amsmath,amssymb}
\setlength{\textwidth}{390pt}
\parindent=0pt
\newcommand{\C}{\mathbb{C}}
\newcommand{\F}{\mathbb{F}}
\newcommand{\N}{\mathbb{N}}
\newcommand{\Q}{\mathbb{Q}}
\newcommand{\R}{\mathbb{R}}
\newcommand{\T}{\mathbb{T}}
\newcommand{\Z}{\mathbb{Z}}

\begin{document}
$$hello
$$

\end{document}
 - Thanks latex.lib and Singular - 
