将数字排版为数学

Question

我有以下代码

\documentclass{article}
\usepackage{amsmath}
\newtheorem{theorem}{Theorem}
\begin{document}
    \begin{theorem}~\\
        Text and something else: $j \in \{1, \ldots, J\}$
    \end{theorem}~\\
    Text and something else: $j \in \{1, \ldots, J\}$
    Text and something else: $\rm j \in \{1, \ldots, J\}$ 
\end{document}

我希望，总是将1输入为J（前两次以斜体显示，最后一次以直立字体显示）。有没有一种自动化的方法 - 比如宏 \one - 可以做到这一点？

---

编辑：

因为我发现这不是我想要的，所以我发布了一个新问题： 将数字排版为数学和数字

Answer 1

你可以，但数学中的数字都是直立排版的，这是一个悠久的传统。

\documentclass{article}
\usepackage{amsmath,amsthm,thmtools}

\declaretheoremstyle[
  spaceabove=\topsep,
  spacebelow=\topsep,
  bodyfont=\itshape,
  break,
]{break}
\declaretheorem[
  style=break,
  name=Theorem,
]{theorem}

\DeclareSymbolFont{italic}{OT1}{\familydefault}{m}{it}
\SetSymbolFont{italic}{bold}{OT1}{\familydefault}{bx}{it}
\DeclareSymbolFontAlphabet{\mathit}{italic}

\DeclareMathSymbol{0}{\mathalpha}{italic}{`0}
\DeclareMathSymbol{1}{\mathalpha}{italic}{`1}
\DeclareMathSymbol{2}{\mathalpha}{italic}{`2}
\DeclareMathSymbol{3}{\mathalpha}{italic}{`3}
\DeclareMathSymbol{4}{\mathalpha}{italic}{`4}
\DeclareMathSymbol{5}{\mathalpha}{italic}{`5}
\DeclareMathSymbol{6}{\mathalpha}{italic}{`6}
\DeclareMathSymbol{7}{\mathalpha}{italic}{`7}
\DeclareMathSymbol{8}{\mathalpha}{italic}{`8}
\DeclareMathSymbol{9}{\mathalpha}{italic}{`9}
\DeclareMathSymbol{!}{\mathclose}{italic}{"21}


\begin{document}

\begin{theorem}
Text and something else: $j \in \{1, \ldots, J\}$
\end{theorem}

Text and something else: $j \in \{1, \ldots, J\}$

Text and something else: $j \in \{\mathrm{1, \ldots, J}\}$ 

\end{document}