Footnote to a footnote

Question

How can I make a footnote to a footnote? E.g.,

Playfair's axiom\footnote{so called in honor of mathematician John Playfair, etc, etc., but was actually discovered by Proclus\footnote{Greek mathematician, etc, etc.}}

Answer 1

Playfair's axiom\footnote{%
so called in honor of mathematician John Playfair, etc, etc.,
but was actually discovered by Proclus\footnotemark}
\footnotetext{Greek mathematician, etc, etc.}

But I'd advise against doing this.

As a bonus, here's an example of how you can really mess with footnotes.

\documentclass{article}
\begin{document}
\footnotetext[4]{We have to go back to the future, Marty!}
Foo\footnote{The footnote to this sentence is true\footnotemark}
\footnotetext{The footnote to this sentence is false\footnotemark[1]} 
more body text\footnotetext[42]{This footnote doesn't appear in the main text}
And more body text\footnote{And we're back to the normal numbering.}
But look where this footnote text ends up!\footnotemark
\end{document}

A few points.

• The footnotes appear in the order the \footnotemarks appear in the text.
• Optional arguments to both \footnotemark and \footnotetext give you control over what number actually appears. (Useful for repeating a footnote if it is relevant again later.
• Everything here should work perfectly with \label and \ref

Answer 2

Use the bigfoot package (as I suggested in the above comment). E.g.:

\documentclass{article}

\usepackage{bigfoot}
\DeclareNewFootnote{Default}
\DeclareNewFootnote{B}[alph]
\MakeSortedPerPage{B}% perhaps also useful to know about

\begin{document}

\verb+bigfoot+%
\footnote{Available on CTAN.} %
improves \LaTeX's%
\footnoteB{Widely known to be less than ideal.} %
footnoting abilities.  \verb+bigfoot+%
\footnote{Available on CTAN.} %
improves \LaTeX's%
\footnoteB{Widely known to be less than ideal.\footnote{See also over
here: one important limitation is that ``Higher-placed footnotes
can't be anchored in inferior ones'' (see \verb+bigfoot.sty+).}} % 
footnoting abilities.

\end{document}