You can add \ShowCommand\lim to your preamble to see the definition of \lim. It'll show
> \lim=robust macro: ->\protect \lim . > \lim =\long macro: ->\mathop {\operator@font lim}. <argument> \lim l.3 \ShowCommand\lim You can then define something similar for \Lim or redefine \lim accordingly:
\makeatletter \NewDocumentCommand{\Lim}{}{\mathop{\operator@font Lim}}% Similar to \lim \RenewDocumentCommand{\lim}{}{\mathop{\operator@font Lim}}% Replace \lim (lim -> Lim) \makeatother Note that this default definition differs from how its defined by other packages. For example, with amsmath, the definition is
> \lim=\protected macro: ->\qopname \relax m{lim}. <argument> \lim l.4 \ShowCommand\lim where \qopname takes 3 arguments, the first of which is the operator text. You could
\NewDocumentCommand{\Lim}{}{\qopname{\relax}{m}{Lim}} \RenewDocumentCommand{\lim}{}{\qopname{\relax}{m}{Lim}} Best would be to use other tools (like mathtools), which help you define operators in a natural way:
\usepackage{mathtools} \let\lim\relax% Remove existing \lim definition \DeclareMathOperator*{\lim}{Lim}% (Re)define \lim \DeclareMathOperator*{\Lim}{Lim}% Define \Lim Here's a complete minimal example:
\documentclass{article} %\ShowCommand\lim %\makeatletter %\NewDocumentCommand{\Lim}{}{\mathop{\operator@font Lim}} %\RenewDocumentCommand{\lim}{}{\mathop{\operator@font Lim}} %\makeatother \usepackage{mathtools} \let\lim\relax \DeclareMathOperator*{\lim}{Lim} \DeclareMathOperator*{\Lim}{Lim} \begin{document} \[ \lim_{n \rightarrow \infty} S_n \qquad \Lim_{n \rightarrow \infty} S_n \] \end{document}