The following code:

```
Inline mode $\|f\|_{H^{-1}}, \|f\|_{_{H^{-1}}}, \|f\|_{_{\scalebox{0.7}{$H^{-1}$}}},\|f\|_{_{\scalebox{0.5}{$H^{-1}$}}}$,
display mode $$\|f\|_{H^{-1}}, \|f\|_{_{H^{-1}}}, \|f\|_{_{\scalebox{0.7}{$H^\{-1}$}}},\|f\|_{_{\scalebox{0.5}{$H^{-1}$}}}$$
```

Results in the following:

I want to have `$H^{-1}$`

as a sub-index, in the first case it is just too big to be a subindex.

I added a second subindex in the second, the H looks good, but the -1 is just too big, in particular the minus sign.

I added scalebox, in the last two cases, which seems to give a better looking result, and it actually scale correctly the term H^{-1}, but I hate to use it, I can see this failing once I have to modify this for other formats, but I'm not sure.

Is there a way to tell that minus sign to scale appropriately with respect to the sub-index level used?

It seems that one way to solve the problem is to correctly set the norms either by grouping or defining a norm command as perfectly shown in some answer.

I still found that the minus sign is too big in what follows:

```
\begin{equation}
\begin{aligned}
&f^{-1}(x) &&L_{f^{-1}}[\eta] \\
&f(x) &&L_{f}[\eta]
\end{aligned}
\end{equation}
```

The "-1" sign takes even more width than the "f" in the first case, in the seconds it gets close to the width of the $L_f$.

I imagine I could use a different symbol, i.e. a minus in $1-2$ could be different that in $-1$.

## Best Answer

(I revised this answer thoroughly after receiving additional comments from the OP.)

I think there are

two issuesthat need to be addressed: One is the spacing around the`-`

("minus") sign when it occurs in scriptscript-style math mode, and the other is the vertical positioning of the subscript formulas that follow a "norm" (double vertical bar) symbol.Regarding the first issue, I suggest you define some macros like this

and then write

`$L_{\finv}[\eta]$`

instead of`L_{f^{-1}}[\eta]`

. Note that this approach simply reduces the amount of whitespace around the scriptscript-style minus symbol. It doesnotreduce the size of either the minus symbol or the digit 1; I'm concerned that reducing the size of the scriptscript-style glyphs would also reduce their basic readability. If you think the compressed`-1`

still takes up too much space, you should probably coming up with new and space-saving notation to denote the inverse of a function. E.g., something like`f*`

or`\bar{f}`

...Regarding the second issue: Note that the formula

`\|f\|_{H^{-1}}`

may be broken down into two sub-formulas:`\|f\|`

and`_{H^{-1}}`

. What you're encountering is that TeX has special rules for placing subscripts that follow a "math atom" such as`\|`

: The subscripts (and superscripts) are set in a cramped mode. While this is OK in most settings, it's clearly not optimal for your use case. I can think of two remedies: Either change the first sub-formula from`\|f\|`

to`{\|f\|}`

, changing its type to "math-ordinary", or -- more LaTeX-ishly -- define a macro called`\norm`

(say) using the machinery of the`mathtools`

package, and then write`\norm{f}`

instead of`{\|f\|}`

.Combining the solutions to the two issues, I think you should write

`\norm{f}_{\Hinv}`

instead of`\|f\|_{H^{-1}}`

.