\documentclass[12pt]{report}
\usepackage[no-math]{fontspec}
\usepackage[
unicode, colorlinks=true, urlcolor=blue, pdfborderstyle={/S/U/W 1}
]{hyperref}
\usepackage[margin=2cm]{geometry}
\geometry{margin=2cm}
\usepackage{hyperref}
\usepackage{amsmath, amssymb, amsthm, array, mathabx}
\usepackage{enumitem}
\usepackage{multirow, bigdelim}
\usepackage{icomma}
\newcommand{\term}[1]{\underline{\smash{#1}}}

\let\temp\phi
\let\phi\varphi
\let\varphi\temp

\let\oldemptyset\emptyset
\let\emptyset\varnothing

\DeclareMathOperator{\lcm}{lcm}
\DeclareMathOperator{\maj}{maj}
\newcommand{\Param}{\mathsf{Param}}

\newcommand{\otto}{\leftrightarrow}
\usepackage{polyglossia}
\setdefaultlanguage[spelling=modern]{russian}
\setotherlanguage{english}
\setmainfont[Renderer=Basic,Ligatures=TeX]{CMU Serif}
\newfontfamily{\cyrillicfont}[Script=Cyrillic,Renderer=Basic,Ligatures=TeX]
{CMU Serif}

\setenumerate{itemsep=-3pt}
\setitemize{itemsep=-3pt}

\theoremstyle{definition}
\newtheorem{define}{Определение}
\newtheorem{eg}{Пример}

\theoremstyle{plain}
\newtheorem{theorem}{Теорема}
\newtheorem{prop}{Предложение}

\begin{document}

\tableofcontents

\end{document}