deletions | additions       diff --git a/header.tex b/header.tex  index 4f7ddb7..17b570a 100644  --- a/header.tex  +++ b/header.tex 
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%\usepackage{amsmath}  %\DeclareMathOperator{\sgn}{sgn} // signum function failed  % see "How to add and manage citations and references in Authorea"   % https://www.authorea.com/users/9932/articles/12628/_show_article  %\usepackage{natbib}  %\bibliographystyle{plainnat}  \usepackage[russian]{babel} %\newcommand{\msun}{\,\mathrm{M}_\odot}  \newtheorem{theorem}{Theorem}  \newtheorem{proof}{Proof}