# How can I force a footnote to appear on the same page as a particular displayed-math environment?

In this example, \footnotemark and \footnotetext are used respectively inside and immediately outside of an align* environment to create a footnote. (Here the equation-numbering system is being abused as a way to place explanatory notes to the right of the working. A footnote is desired here because the explanatory note in question is excessively long and is forced onto its own line, which looks ugly.) However, because I have contrived to put the align* environment at the bottom of the page, the footnote is getting shifted onto the following page. This is undesirable. It would be much better if the footnote were on the same page as the align* environment.

(Straightforward use of \footnote does not work in the align* environment. The standard solution, as described in answers to other TeX/LaTeX Stack Exchange questions, is to use \footnotemark and \footnotetext as seen here. But just doing this does not address this issue.)

\documentclass[a4paper, reqno]{amsart}

\newtheorem{proposition}{Proposition}
\newcommand{\tie}{\bowtie}
\newcommand{\ordtie}{\mathord{\tie}}

\begin{document}

Here is some vertical space to force the align* environment to the

\begin{proposition}
Behold: a proposition.
\end{proposition}

\begin{proof}
We first check that $f$ satisfies both parts of Definitions (number).
For (i), let $v \in V_{(G / \ordtie) / \ordtie''}$. Then
$v = \big[[v']_{\tie}\big]_{\tie''}$ for some $v' \in V_G$, and we have
\begin{align*}
\pi_{G / \ordtie'}f(v) &= \pi_{G / \ordtie'}\big(f\b(){\b[]{[v']_{\tie}}_{\tie''}}\big)
\\ &= \pi_{G / \ordtie'}\big([v']_{\tie'}\big)
\tag{by Proposition (number)}
\\ &= \pi_G(v')
= \pi_{G / \ordtie}\big([v']_{\tie}\big)
= \pi_{(G / \ordtie) / \ordtie''}\big(\big[[v']_{\tie}\big]_{\tie''}\big)
\tag{\footnotemark}
\\ &= \pi_{(G / \ordtie) / \ordtie''}(v),
\end{align*}
\footnotetext{Here we are using (three times) the definition from
Definitions (number) of the parity map of a quotient graph.}
as required. For (ii), let $\{u, v\} \in U_{(G / \ordtie) / \ordtie''}$;
then there exists $\{u', v'\} \in U_G$ such that
$u = \big[[u]_{\tie}\big]_{\tie''}$ and $v = \big[[v]_{\tie}\big]_{\tie''}$. We have
$\text{some more displayed mathematics, I daresay.}$
And that's all.
\end{proof}

\end{document}


How might I force the footnote to be on the same page as the \align* environment, given that the \footnotetext command cannot be placed inside the environment (for the same reason, I assume, that simply using \footnote does not work inside the environment)?

-
This is not recommended as it will be confusing for the readers. I'd rather recommend directly writing In the second to last line we are using (three times) ... – daleif Sep 12 '13 at 8:58
given the size of the footnote, using \enlargethispage probably isn't going to do it. a non-recommended possibility is to allow breaks within the align* and explicitly encourage one just before the line that requires the footnote. – barbara beeton Sep 12 '13 at 14:09