By default operator space didn't come for super and subscripts which is correct in general. Refer the below code:

```
\documentclass{book}
\begin{document}
\[
a+b\sum+\int_{a+b\quad a=b}
\]
\end{document}
```

But any one can explain why this was fixed? I need to know this in detail…

## Best Answer

By default binary operators such as + get a

`\medmuskip`

space either side, and relations such as`=`

get`\thickmuskip`

but this additional space is not added in scriptstyle and scriptscriptstyle settings. This is not configurable by TeX macros, it is built into the TeX sources as part of its math layout.A

`\quad`

is just defined to be`\hskip1em`

so it is not really a math-aware space it is 1em in the text font current before the math started. You can use`\nonscript\quad`

if you really need to use a quad that vanishes in subscripts.or use a math space such as

`\:`

that adjusts to the subscript font size:`\:`

is`\mskip\medmuskip`

and skips specified in`mu`

units are relative to the current math style.