定义数学概念

Question

我想知道如何修复：

Namely the study of arrows in~$\Cat_{/\cal{E}}$.

错误是

Undefined control sequence.

 < recently read > \Cat 

l.46 ... view. Namely the study of arrows in~$\Cat _{/\cal{E}}$.

我在用

\usepackage[english,francais]{babel}

\usepackage{amssymb,url,xspace,smfthm}

\usepackage[all,cmtip]{xy}

Answer 1

无法抗拒。

\documentclass{article}
\usepackage{tikzsymbols}
\begin{document}
The theory of arrows from a topological point of view.
Namely the study of arrows in~$\Cat_{/\mathcal{E}}$.
\end{document}

更现实的版本，其输出与论文中所述一致：

\documentclass{article}
\usepackage{calrsfs}
\newcommand*{\Cat}{\mathbf{Cat}}
\begin{document}
The theory of arrows from a topological point of view.
Namely the study of arrows in~$\Cat_{/\mathcal{E}}$.
\end{document}