\documentclass[11pt]{article}
\usepackage{epsfig}

\newcommand{\BC}{\mathbb{C}}
\newcommand{\BR}{\mathbb{R}}
\newcommand{\BZ}{\mathbb{Z}}
\newcommand{\BN}{\mathbb{N}}
\newcommand{\BQ}{\mathbb{Q}}
\def\di{\displaystyle}

\input{amssym}
\input{epsf}
\textwidth = 15 cm \textheight = 22 cm \oddsidemargin = 0 cm
\evensidemargin = 0 cm \topmargin = -1 cm \topmargin = 0 cm
\parskip = 2.5 mm
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\newtheorem{preqst}{{\bf Question}}
\renewcommand{\thepreqst}{{\arabic{preqst}}}
\newenvironment{question}{\begin{preqst}{\hspace{-0.5
em}{\bf.}}}{\end{preqst}}
%
\newtheorem{preex}{{\bf Example}}
\renewcommand{\thepreex}{\arabic{preex}}
\newenvironment{example}{\begin{preex}{\hspace{-0.5
em}{\bf.}}}{\end{preex}}
%
\newtheorem{presol}{{\bf Solution}}
\renewcommand{\thepresol}{\arabic{presol}}
\newenvironment{solution}{\begin{presol}{\hspace{-0.5
em}{\bf.}}}{\end{presol}}
%
\newtheorem{preproof}{{\bf Proof.}}
\renewcommand{\thepreproof}{}
\newenvironment{proof}[1]{\begin{preproof}{\rm
               #1}\hfill{$\rule{2mm}{2mm}$}}{\end{preproof}}
%
\newtheorem{predef}{{\bf Definition}}
\renewcommand{\thepredef}{{\arabic{predef}}}
\newenvironment{definition}{\begin{predef}{\hspace{-0.5
em}{\bf.}}}{\end{predef}}
%
%
\newcommand{\FTC}[1]{The fundamental Theorem of Calculus, Part #1}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



\begin{document}
\title{...}
\author{... }
\date{2 May 2015}
\maketitle
\begin{abstract}

\end{abstract}

\section{Topological space}


$\mathbb{N}$
















%\bibliographystyle{abbrv}
%\bibliography{bibref}
\begin{thebibliography}{99}
\bibitem{Mankerz} {\it James R.Munkers And Prentice-Hall}
\newblock {\em First Lesson Of Topology , 1975}.
\end{thebibliography}
\end{document}