LaTeX Forum

\documentclass{scrreprt}

\usepackage{mathrsfs,amssymb}
\usepackage[intlimits]{empheq}
\usepackage{theorem}
\mathchardef\Rightarrow="3229
\DeclareMathAlphabet{\mathcal}{OMS}{cmsy}{m}{n}

\begin{document}

\begin{equation}
\epsilon_B = \frac{\int_{\lambda_1}^{\lambda_2} M_\lambda \left(\lambda,T\right) d\lambda}{\int_{\lambda_1}^{\lambda_2} M_{\lambda,S} \left(\lambda,T\right) d\lambda}+\int_{\lambda_1}^{\lambda_2} M_\lambda \left(\lambda,T\right) d\lambda
\end{equation}

\end{document}

\expandafter\def\expandafter\int\expandafter{\int\limits}

\DeclareOption{intlimits}{\let\ilimits@\displaylimits}

\usepackage{amsmath}
\makeatletter
\let\ilimits@\limits
\makeatother