\documentclass[12pt, twoside, leqno]{article}
% Modif. March 12, 2013
% Send comments to publ@impan.pl
% Using pdflatex is preferred
\usepackage{amsmath,amsthm}
\usepackage{amssymb}
%% Optional, but useful:
\usepackage{enumerate}
%% Add only when there are figures:
\usepackage{graphicx}
%% If you are using letters of the Polish alphabet, add
%\usepackage[T1]{fontenc}
%% E.g. the name "Zoladz" is then coded \.Zo{\l}\k{a}d\'z
%% In the running head, replace first names by initials
%% and give an abbreviation of the title.
\pagestyle{myheadings}
\markboth{A. Kowalska and J. K. Nowak}{Sample paper}
%%%%%
%% Numbered objects of "theorem" style (text italicized).
%% Below, the optional parameters indicate that all objects are numbered together, and "by section".
%% However, you are welcome to use any other numbering system of your choice, as well as your own abbreviations.
\newtheorem{thm}{Theorem}[section]
\newtheorem{cor}[thm]{Corollary}
\newtheorem{lem}[thm]{Lemma}
\newtheorem{prop}[thm]{Proposition}
\newtheorem{prob}[thm]{Problem}
%% A numbered theorem with a fancy name:
\newtheorem{mainthm}[thm]{Main Theorem}
%% Numbered objects of "non-theorem" style (text roman):
\theoremstyle{definition}
\newtheorem{defin}[thm]{Definition}
\newtheorem{rem}[thm]{Remark}
\newtheorem{exa}[thm]{Example}
%% An unnumbered object:
\newtheorem*{xrem}{Remark}
%% Equations numbered by section (optional):
\numberwithin{equation}{section}
%%%%%%%%%%% For IMPAN journals:
\frenchspacing
\textwidth=13.5cm
\textheight=23cm
\parindent=16pt
\oddsidemargin=-0.5cm
\evensidemargin=-0.5cm
\topmargin=-0.5cm
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%% Put your macros here:
\newcommand{\length}{\operatorname{length}}
%%%%%%%%%%%%%
\begin{document}
%%%%% To ease editing, for IMPAN journals add:
\baselineskip=17pt
%%%%%%%%%%%%%%%%
\title{A sample paper for IMPAN journals}
\author{Anna Kowalska\\
Institute of Mathematics\\
Polish Academy of Sciences\\
00-956 Warszawa, Poland\\
E-mail: kowalska@impan.pl
\and
Jan Krzysztof Nowak\\
Institute of Mathematics\\
Warsaw University\\
02-097 Warszawa, Poland\\
E-mail: jk.nowak@mimuw.edu.pl}
\date{}
\maketitle
%% Classification and key words; note that the 2010 classification is used:
\renewcommand{\thefootnote}{}
\footnote{2010 \emph{Mathematics Subject Classification}: Primary XXXX; Secondary YYYY.}
\footnote{\emph{Key words and phrases}: aaaa, bbbb, cccc.}
\renewcommand{\thefootnote}{\arabic{footnote}}
\setcounter{footnote}{0}
%%%%%%%%
\begin{abstract}
A template for articles in IMPAN journals in the \texttt{article} style. Using \texttt{pdflatex} is strongly preferred.
\end{abstract}
\section{Introduction}
You can use this file as a template when submitting your paper to one of the IMPAN journals (except Dissertationes Mathematicae and Banach Center Publications, for which style files exist).
The format of this file is \textbf{not} the exact final printed format (for example, the latter is scaled down, and line breaks will most often be different), but it is convenient for editing purposes.
\section{Theorems etc.}
The statements of theorems, propositions etc. are set in
italics. In definitions, only the term being defined is emphasized. Remarks
and examples are set in roman type.
\begin{defin}
A system $S$ is said to be \emph{self-extensional} if
$S \in B$.
\end{defin}
\begin{prob}
Is $A+B=C$ true?
\end{prob}
%% Note that in the example below, the braces { } around \cite are necessary (due to nested optional parameters)
\begin{thm}[Identity Principle, see also {\cite[Theorem 5]{HillDow}}]\label{T:1}
If $A=B$, then the following conditions are equivalent:
\begin{enumerate}[\upshape (i)]
\item first item,
\item second item,
\item third item.
\end{enumerate}
\end{thm}
\begin{proof} We only prove (i)$\Rightarrow$(ii). Observe that
\begin{align}\label{E:1}
\big(\tfrac{1}{2}(y+\length_iA_i)\big)^2
&= \binom{a+b}{c-d}\\
&\quad + \Big(\prod_{i=1}^n A_i\Big)^2 + \bigg(\frac{u}{v}\bigg)^n\notag\\
&\overset{\alpha}=
\begin{cases}
\sqrt[3]{2/\!\sin x} &\text{if $x \in (0, \pi)$,}\\
0 &\text{otherwise.}\notag
\end{cases}
\end{align}
Now apply induction on $n$ to \eqref{E:1}.
\end{proof}
\begin{xrem}
Theorem~\ref{T:1} was independently proved in \cite{Kow}.
\end{xrem}
\begin{mainthm}
Here comes the statement of a numbered theorem with a fancy name.
\end{mainthm}
Note that formulas in IMPAN journals are left-numbered.
For many examples of codes of multiline formulas, see
\texttt{http://journals.impan.pl} (``For authors'').
The \texttt{eqnarray} construction leads to well-known mistakes---if you have learnt it, just forget it.
Do not leave ``overflows'' in formulas; if the formula is too wide, break it yourself into lines or, e.g., shorten it by introducing some symbols.
Do not re-invent {\LaTeX}; before using your own construction or creating a new symbol
look up Gr\"atzer \cite{Gratzer}---most probably, your intended construction or symbol is already there.
Add small spaces \texttt{\textbackslash,} only exceptionally, e.g. before differentials.
\section{Figures}
Preferably, figures should be prepared as pdf, jpg or eps files.
All figures will be printed black and white; colours will only appear in the online version.
Avoid very thin lines, and check whether all fonts used are embedded.
Remember that sometimes figures have to be scaled, and then the lettering is scaled too; therefore, very small lettering should be avoided.
\begin{figure}[h]
\caption{A figure caption}
\end{figure}
\subsection*{Acknowledgements}
This research was partly supported by NSF (grant no. XXXX).
\begin{thebibliography}{HD}
%% Use the widest label as parameter.
%% Reference items can be numbered or have labels of your choice, as below.
%% In IMPAN journals, only the title is italicized; boldface is not used.
%% Our software will add links to many articles; for this, enclosing volume numbers in { } is helpful
%% Do not give the issue number unless the issues are paginated separately.
%%%%%%%%%%% To ease editing, use normal size:
\normalsize
\baselineskip=17pt
%%%%%%%%%%%%%
\bibitem[G]{Gratzer} G. Gr\"atzer,
\emph{More Math into \LaTeX},
4th ed., Springer, Berlin, 2007.
\bibitem[HD]{HillDow} R. Hill and A. Dow,
\emph{A ground-breaking achievement},
J.~Differential Equations {15} (1982), 197--211.
\bibitem[K]{Kow} J. Kowalski,
\emph{A very interesting paper},
in: Algebra, Analysis and Beyond (Nowhere, 1973),
E.~Fox et al. (eds.),
Lecture Notes in Math. 867, Springer, Berlin, 1974, 115--124.
\bibitem[N]{Nov} A. S. Novikov,
\emph{Another fascinating article},
Uspekhi Mat. Nauk {23} (1980), no.~3, 112--134 (in Russian);
English transl.: Russian Math. Surveys 23 (1980), 572--595.
\bibitem[R]{Russ} B. Russell,
\emph{A new theorem},
arXiv:2012.9876.
\end{thebibliography}
\end{document}