答案1
这就是所谓的拥挤风格,在 luatex 中您可以摆脱它,但在经典 tex 中您需要重新启动嵌套的数学列表才能避免它。
\documentclass{article}
\begin{document}
This looks nice: $E'$,
and while this is okay: $E'^2$,
this is probably better: ${E'}^2$,
but this is ugly: $\sqrt{E'^2}$,
and this as well: $\sqrt{{E'}^2}$.
But $\sqrt{\hbox{$E'^2$}}$.
\end{document}
或者您可以调整字体参数,使拥挤的设置不那么拥挤......