My very own LaTeX style

preamble.tex

% Language and page style
\documentclass[a4paper,12pt]{article}
\pagestyle{empty}
\usepackage{color}
\usepackage[utf8]{inputenc}
\usepackage[T2A]{fontenc}
\usepackage[russian]{babel}

% Auxiliary pacckages
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{enumitem}
\usepackage{etex}
\usepackage{enumitem}
\usepackage{graphicx}
\usepackage{mathtools}
%\usepackage{minted} % Use only if you need highlighted code snippets
\usepackage{qtree}
\usepackage{verbatim}

% In Russian ;)
\newtheorem{theorem}{Теорема}
\newtheorem{definition}{Определение}
\newtheorem{proposal}{Предложение}
\newtheorem{lemma}{Лемма}
\newtheorem{remark}{Замечание}
\newtheorem{example}{Пример}

% Useful (and common!) operators
\renewcommand{\O}{\mathcal{O}}
\renewcommand{\C}{\mathbb{C}}
\newcommand{\R}{\mathbb{R}}
\newcommand{\Q}{\mathbb{Q}}
\newcommand{\N}{\mathbb{N}}
\newcommand{\eps}{\varepsilon}
\newcommand{\Ra}{\Rightarrow}
\newcommand{\ra}{\rightarrow}
\newcommand{\Lra}{\Leftrightarrow}
\newcommand{\Sum}{\sum \limits}
%\newcommand{\cc}{\mintinline{c++}}
\DeclareMathOperator{\Ima}{Im}
\DeclareMathOperator{\rk}{rk}

\renewcommand{\labelenumii}{\arabic{enumii}}

\def\multiset#1#2{\ensuremath{\left(\kern-.3em\left(\genfrac{}{}{0pt}{}{#1}{#2}\right)\kern-.3em\right)}}

% Smaller margins
\textwidth=160mm
\hoffset=-15mm
\textheight=240mm
\voffset=-20mm

% What is it I don't even
\def\changemargin#1#2{\list{}{\rightmargin#2\leftmargin#1}\item[]}
\let\endchangemargin=\endlist