答案1
也许是这样的?
\documentclass{article}
\usepackage{stmaryrd}
\usepackage{trimclip}
\newlength{\nnearrowheight}
\newlength{\ssearrowheight}
\settoheight{\nnearrowheight}{$\nnearrow$}
\settoheight{\ssearrowheight}{$\ssearrow$}
\newcommand{\bottomofnnearrow}{\makebox{\clipbox{0pt 0pt 0pt {.5\totalheight}}{$\nnearrow$}}}
\newcommand{\topofnnearrow}{\raisebox{.37\nnearrowheight}[.5\nnearrowheight][0pt]{\makebox{\clipbox{0pt {.5\totalheight} 0pt 0pt}{$\nnearrow$}}}}
\newcommand{\bottomofssearrow}{\makebox{\clipbox{0pt 0pt 0pt {.5\totalheight}}{$\ssearrow$}}}
\newcommand{\topofssearrow}{\raisebox{.37\ssearrowheight}[.5\ssearrowheight][0pt]{\makebox{\clipbox{0pt {.5\totalheight} 0pt 0pt}{$\ssearrow$}}}}
\newcommand{\upweakto}{\mathrel{%
\bottomofnnearrow%
\hspace*{-.7pt}\makebox[0pt]{$-$}\hspace*{.35pt}%
\topofnnearrow\hspace*{-.65pt}%
}}
\newcommand{\downweakto}{\mathrel{%
\hspace*{-.65pt}\topofssearrow%
\hspace*{-.7pt}\makebox[0pt]{$-$}\hspace*{.35pt}%
\bottomofssearrow%
}}
\begin{document}
\[ x_n \upweakto x \qquad y_n \downweakto y \]
\end{document}