1:

\newcommand{\Abb}{\operatorname{Abb}}

1:
2:
3:
4:
5:
6:
7:
8:

\documentclass[a4paper,10pt]{article}
\usepackage{amsmath}
\newcommand{\Abb}{\operatorname{Abb}}
\begin{document}
\tableofcontents
\section{Test von $\Abb $}
text
\end{document}

1:

\contentsline {section}{\numberline {1}Test von $\operatorname {Abb}$}{1}

1:

\contentsline {section}{\numberline {1}Test von $\Abb $

1:

\section{Test von $\protect\Abb$}

1:
2:
3:
4:
5:
6:
7:
8:
9:
10:
11:
12:
13:

\documentclass[11pt,parskip=full]{scrartcl}

\usepackage{amsmath}  								% Mathe-Improvements

\DeclareMathOperator{\discup}{\mathbin{\dot{\cup}}}
\DeclareMathOperator*{\bigdiscup}{\mathbin{\dot{\bigcup}}}

\DeclareMathOperator{\inter}{\mathring}
\DeclareMathOperator{\cl}{\overline}

\begin{document}
$\inter M$ und $\cl M$ geht nicht, $A\discup B$ und $\bigdiscup\limits_{\alpha\in I}~U_{\alpha}$ aber schon.
\end{document}