将两个数学符号直接设置在彼此上方并垂直对齐

Question

我正在排版 Neyman Pearson 决策规则，想将大于>和小于<符号直接设置在彼此上方。我试过了\overset，但结果两个符号并没有垂直对齐到中间。

Answer 1

当然，总是\gtrless有

\usepackage{amssymb}% http://ctan.org/pkg/amssymb

如果你不想使用包，你可以自己“覆盖”符号：

\documentclass{article}
\newcommand{\npsym}{%
  \mathrel{\ooalign{\raisebox{.6ex}{$>$}\cr\raisebox{-.6ex}{$<$}}}
}
\begin{document}
Here is some text. Here is some text. Here is some text. Here is some text.
See, for example, $x\npsym y$. Here is some text. Here is some text. Here is some text.
Here is some text. Here is some text. Here is some text. Here is some text.
\end{document}​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

看\subseteq+\circ作为单个符号（“开子集”）参加 短期课程\ooalign。

Answer 2

如果\grtless没有的话，可以用表格来定义；为了提高效率，最好使用原始命令：

\documentclass{article}

% This won't do anything if amssymb is loaded first
\providecommand{\gtrless}{
  \mathrel{% it's a relation
  \smash{% we don't want that it influences the interline spacing
  \vcenter{% the symbol will be vertically centered
    \offinterlineskip % no interline skip here
    \ialign{% build a table
       \hfil##\hfil\cr % just one centered column
       $>$\cr % first row
       \noalign{\kern-.3ex}% shorten the vertical distance
       $<$\cr % second row
    }% end of the \ialign
  }% end of \vcenter
  }% end of \smash
  \vphantom{>}% pretend it's as high as a >
  }% end of \mathrel
}

\begin{document}
Here is some text. Here is some text. Here is some text. Here is some text.
See, for example, $x\gtrless y$. Here is some text. Here is some text. Here is some text.
Here is some text. Here is some text. Here is some text. Here is some text.
\end{document}