Particularly in the humanities, authors can have multiple classes of footnotes, including having footnotes of footnotes. The package bigfoot extends LaTeX’s default footnote mechanism in many ways, including allow these two, as in this example.
\usepackage{bigfoot} % in preamble
\DeclareNewFootnote{Default}
\DeclareNewFootnote{from}[alph] % create class \footnotefrom{}
...
The third theorem is a partial converse of the
second.\footnotefrom{%
First noted in Wilson.\footnote{Second edition only.}}
© 2007–2018 Karl Berry
Public Domain Software
http://latexref.xyz/Footnotes-of-footnotes.html