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I'm writing a financial math book. The book is obviously filled with equations, numbered this way:

Chapter 1

Equation 1.1

Equation 1.2

...

Chapter 2

Equation 2.1

Equation 2.2

...

There are equations which demonstration is a bit tougher or more tedious, so I only present the formula in the text and relegate the formal proof to the footnotes. I have a problem with numbering equations in the footnotes though. If I let LaTeX automatically number them, it will assign a double numbering scheme, like in the text (chapter number + sequential number of the equation in the chapter). I would like to reset the numbering every footnote, like either:

  1. Footnote text

Equation 1

Equation 2

...

Or:

  1. Footnote text

Equation I

Equation II

...

I tried using \setcounter{equation}{0}, but unfortunately it just resets the two number scheme to 1.1, 1.2...

Is there any way to use a different numbering scheme in the footnotes? Either 1, 2, 3..., I, II, III..., A, B, C... ?

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    Welcome to TeX SX! The mathtools defines a \ \newragform` and a \usetagform commands, which might help.
    – Bernard
    Oct 12, 2022 at 18:53
  • How are the footnotes numbered within the document? Consecutively throughout the book, or is there a restart at each chapter? Would it be ok to number the footnote-related equations separately for each footnote? E.g., could the equations in footnote 5 be numbered as [5.a], [5.b], etc, equations in footnote 7 be numbered as [7.a], [7.b], etc, and so on?
    – Mico
    Oct 12, 2022 at 19:27
  • Thank you for your comment Mico! Yeah, I think that would be ok! My only concern is not mixing up numbering inside of text and inside of footnotes Oct 12, 2022 at 20:04
  • 1
    Why footnotes? Add an appendix.
    – egreg
    Oct 12, 2022 at 21:28

1 Answer 1

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The following solution may be of interest to you: Equations in footnotes are numbered as (<footnote>-<alphabetic-fneq-counter-rendered-in-smallcaps>), where fneq is a counter that's separate from the equation counter. Note the use of - instead of . to "connect" the numbers.

I suggest you use only unnumbered display math environments in the footnotes and provided \dotag instructions in those equations you want to see numbered. \dotag takes a mandatory argument -- the label to be applied, to enable cross-referencing.

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\documentclass[oneside]{book}
\usepackage{amsmath}

\newcounter{fneq}
\counterwithin{fneq}{footnote}
\renewcommand\thefneq{\thefootnote-\textsc{\alph{fneq}}}

\newcommand\dotag[1]{\refstepcounter{fneq}\label{#1}\tag{\thefneq}}

\usepackage[noabbrev]{cleveref} % optional

\begin{document}


\chapter{Uno}
\setcounter{footnote}{4} % just for this example
\begin{equation} 1+1=2 \label{eq:1_1}\end{equation} 
aaa.\footnote{%
A moment's reflection shows that
\begin{align*} 
0+0&=0    \dotag{fneq:aa_1} \\
\intertext{and}
0-0&=0\,. \dotag{fneq:aa_2} 
\end{align*}
} 
bbb.\footnote{%
Pythagoras showed that
\[ a^2+b^2=c^2\,. \dotag{fneq:bb_1} \]
}
\begin{equation} 2+2=4 \label{eq:1_2}\end{equation}

\chapter{Due}
Cross-references to \cref{fneq:aa_1,fneq:aa_2,,fneq:bb_1,eq:1_2,eq:1_1}.
    
\end{document}
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    Thank you so much for your useful explanation! Oct 14, 2022 at 16:54

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