\documentclass[11pt,a4paper,reqno]{article}
\usepackage{amssymb,amsfonts,amsmath}
\usepackage{geometry}
%\usepackage{makeidx}
\usepackage{times}

\newtheorem{proposition}{Proposition}
\newtheorem{lemma}{Lemma}
\newtheorem{theorem}{Theorem}
\newtheorem{corollary}{Corollary}
\newtheorem{definition}{Definition}
\newtheorem{remark}{Remark}
\newtheorem{problem}{Problem}


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\begin{document}


\begin{center}
\Large
\textsc{Abstract preparation and submission guidelines}
\\[2mm]\normalsize
Markus Holzmann, 
\emph{Graz, Austria}
\index{Siegl, P.}
\\ 
Petr Siegl.
\emph{Graz, Austria}
\index{Siegl, P.}
\end{center}

Please, do not use your own macros and cross-reference commands except  \verb@\cite{label}@, and do not change text before  \verb@\begin{document}@.
Your abstract should not exceed \textbf{one page}.

You may use all standard environments marked by $*$ for typing numbered and unnumbered equations  in your abstract. Please use the command \verb@\tag{number}@ to type numbered equations.  E.g.:
\begin{equation*}
-\Delta u = f.\tag{1}
%This equation is numbered. To make it unnumberad you should omit command \tag(1).
\end{equation*}

You may use environments \verb@proposition@, \verb@lemma@, \verb@theorem@, \verb@corollary@, \verb@definition@, \verb@remark@, \verb@problem@. E.g.:
\begin{theorem}
The operator $A$ has purely discrete spectrum.
\end{theorem}



The list of references should be adjusted with \verb@\thebibliography@ environment. Please, begin all labels in the command \verb@\bibitem@ from YOUR name. In the case of two or three authors of the abstract, use the name of the first one. E.g., for David Hilbert they are dhilbert1, dhilbert2, dhilbert3. Please use the command \verb@\cite{label}@ to cite the items. E.g., we have used the command \verb@\cite{dhilbert2}@ to cite \cite{dhilbert2} above in this file.

%%%%%%%%%%%%%

% Please, begin all labels in the command \verb@\bibitem@ from YOUR name. In the case of two or three authors of the abstract, use the name of the first one. E.g., for David Hilbert they are dhilbert1, dhilbert2, dhilbert3.  

\begin{thebibliography}{99}
\footnotesize

\bibitem{dhilbert1}
T.~Kato, 
Perturbation theory for linear operators, 
Springer-Verlag, New York, 1966.

\bibitem{dhilbert2}
G.C.~Papanicolaou, S.R.S.~Varadhan, 
Diffusion in regions with many small holes. Stochastic differential systems (Proc. IFIP-WG 7/1 Working Conf., Vilnius, 1978), pp. 190–206, Lecture Notes in Control and Information Sci., 25, Springer, Berlin-New York, 1980. 


\bibitem{dhilbert3}
J.~Rauch, M.~Jeffrey, 
Potential and scattering theory on wildly perturbed domains, 
J. Funct. Anal. 18 (1975), 27--59.


 
\end{thebibliography}

 
\end{document}


