答案1
我尝试了第 85 页底部的公式谷歌图书
\documentclass{article}
\usepackage{mathtools}
\DeclareRobustCommand{\DPiA}{\mathbf{II}}
\DeclareRobustCommand{\DPiB}{\mathbf{I\mspace{-1mu}I}}
\DeclareRobustCommand{\DPiC}{{\mathrlap{\amalg}\Pi}}
\begin{document}
First version:
\[
A \rightarrow (\Pi = \DPiA(R) \leftrightarrow \mathsf{R}(\Pi) = R)
\]
Second version:
\[
A \rightarrow (\Pi = \DPiB(R) \leftrightarrow \mathsf{R}(\Pi) = R)
\]
Third version:
\[
A \rightarrow (\Pi = \DPiC(R) \leftrightarrow \mathsf{R}(\Pi) = R)
\]
\end{document}
选择你最喜欢的一个,我更喜欢第三个。