weired dash in references

In the abstract body text (jason file) I got "... clock$^3$$^−$$^5$". This persists after running gca-tex on it. pdflatex then breaks:
```
! Missing { inserted.

\begingroup
l.105 ... They exhibit a circatidal clock$^3$$^−
$$^5$ plays a role in thei...
```
If I replace the dash (which is not a normal dash) by a normal dash or by `{--}` it works.

Start with the gca-tex processing of the abstract body text from the JSON input and trace how the nonstandard dash is emitted into LaTeX. Reproduce the failure with pdflatex using the reported text, then verify that the generated output handles the dash without the Missing { inserted error.

Written by the indexing model from the issue text.