得益于amsmath的\allowdisplaybreaks宏，可以让分页符随意放置在任何位置，甚至可以放置在多行方程的中间（例如来自环境align）。
- 优点
\allowdisplaybreaks：否则（禁止在多行方程式中间分页），文档很可能包含非常丑陋的未满垂直盒子。 - 缺点
\allowdisplaybreaks：“我们对这个案例中的所有方程式都没有看法”，正如仅允许从偶数页到奇数页的显示中断。
为了减少上述缺点，一种解决方案是在多行方程式中出现分页符时添加边注（包含类似“方程式在下一页后面”的内容）。
是否有可能实现这样的结果，例如对于环境而言align？
编辑
这是我想要实现的 MWE，手动获取很容易，但我希望自动获取。它包含一个脚注和一个浮动图，以指出位于页面底部（右侧）的边注是不够的，因为它可能远离方程断开的线。
\documentclass{report}
\usepackage{amsmath}
\usepackage{mwe}
\usepackage{marginnote}
\usepackage[papersize={130mm,140mm},margin=30mm]{geometry}
\allowdisplaybreaks
\newcommand{\eqcont}{\tiny(Cont.\ next page)}
\begin{document}
Foo\footnote{\tiny\lipsum[1]}
\begin{multline}
x = abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz\marginnote{\eqcont} \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz
\end{multline}
\begin{figure}[b]
\centering
\includegraphics[height=1cm]{image-a}
\caption{A nice figure}
\label{nice-figure}
\end{figure}
\begin{align}
1 + 1 & = 2 \\
2 + 1 & = 3 \\
3 + 1 & = 4 \\
4 + 1 & = 5 \\
5 + 1 & = 6 \\
6 + 1 & = 7\marginnote{\eqcont} \\
7 + 1 & = 8 \\
8 + 1 & = 9 \\
9 + 1 & = 10
\end{align}
\end{document}
答案1
也许是这样的：
我已经使用过\appto（和\csappto）来自电子工具箱ifInAlign在align和环境中设置和取消设置布尔标志align*（其他环境可以以完全相同的方式完成）。这个想法是，\ifInAlign当您在环境中时为真align，否则为假。然后，使用背景包我为每个页面添加了“背景文本”，如下所示
\ifInAlign\tiny Equation continues...\fi
也就是说，Equation continues...当Align环境延伸到整个页面时我们才能看到东西，否则我们什么也看不到。
完整代码如下：
\documentclass{article}
\usepackage{amsmath}
\usepackage[papersize={100mm,80mm}, margin=20mm]{geometry}% to get short pages
\newif\ifInAlign\InAlignfalse% to determine if we're inside an align environment
\usepackage{etoolbox}
\appto\align{\global\InAligntrue}% InAlign true at start of align
\csappto{align*}{\global\InAligntrue}% InAlign true at start of align*
\appto\endalign{\global\InAlignfalse}% InAlign false at end
\usepackage{background}% add continued note when InAlign
\backgroundsetup{angle=0,
scale=1,
color=black,
position={0.68\textwidth,-0.95\textheight},
contents={\ifInAlign\tiny Equation continues...\fi}
}
\everymath{\allowdisplaybreaks[4]}% turn on display breaks, always!
\begin{document}
\begin{align}
0 + 1 &= 1\\% some deep multi-lined aligned equations
1 + 1 &= 2\\
2 + 1 &= 3\\
3 + 1 &= 4\\
4 + 1 &= 5\\
5 + 1 &= 6\\
6 + 1 &= 7\\
7 + 1 &= 8\\
8 + 1 &= 9\\
9 + 1 &= 10\\
10 + 1 &= 11\\
11 + 1 &= 12\\
12 + 1 &= 13\\
13 + 1 &= 14\\
14 + 1 &= 15\\
15 + 1 &= 16\\
16 + 1 &= 17\\
17 + 1 &= 18\\
18 + 1 &= 19\\
19 + 1 &= 20
\end{align}
\end{document}
为了保证公式跨页显示，我使用了几何学包使得页面尺寸非常小。
答案2
好的，我成功了，希望我没有忘记可能的副作用。以下 MWE 包含解释该方法的注释（稍后，我将尝试给出expl3它的风味）。
编辑
\\我的原始代码在外部环境的文本模式下使用时出现错误，tabular因为在多行方程环境的末尾，\\它被全局重新定义为这些环境内的那个，这与默认值不同。
\documentclass{report}
\usepackage{amsmath}
\usepackage{mwe}
\usepackage{etoolbox}
\usepackage{refcount}
\usepackage{xifthen}
\usepackage{marginnote}
\usepackage[papersize={130mm,140mm},margin=30mm]{geometry}
\allowdisplaybreaks
\newcommand{\eqcont}{\tiny(Cont.\ next page)}
% Each multiline equation will have a unique number.
\newcounter{multilineeq}
% Each line of a multiline equation will have a unique number (local
% to the multiline equation).
\newcounter{lineofmultilineeq}[multilineeq]
\makeatletter
% We globally store the original double backslash in a macro
\global\let\original@double@backslash\\
% We define the patched macro of the double backslash one
\newcommand{\patched@double@backslash}{%
% We increment the counter of the current line.
\stepcounter{lineofmultilineeq}%
% We set the label of the current line.
\ltx@label{\lineofmultilineeq@label}%
% If (and only if) the pageref of the next line if greater than the
% current line's one, we insert a marginal note telling the equation
% continues on next page.
\ifthenelse{%
\cnttest{%
\getpagerefnumber{\nextlineofmultilineeq@label}%
}{>}{%
\getpagerefnumber{\lineofmultilineeq@label}%
}%
}{%
\marginnote{\eqcont}%
}{}
% We break the line with the original double backslash macro.
\original@local@double@backslash%
}
% We define a hack to be applied at the beginning of each multiline equation
% environment (currently, only `align(*)' and `multline(*)').
\def\beginhack{%
% We set the unique number that has the current multiline equation.
\stepcounter{multilineeq}
% The number that has the 1st line of the current multiline equation is 1.
\stepcounter{lineofmultilineeq}
% We globally define the strings of the labels identfying:
% - the current line,
% - the line following the current one,
% of the current multiline equation.
\gdef\lineofmultilineeq@label{multilineeq-\themultilineeq-line-\thelineofmultilineeq}
\gdef\nextlineofmultilineeq@label{multilineeq-\themultilineeq-line-\the\numexpr\thelineofmultilineeq+1}
% We set the label of the current line.
\ltx@label{\lineofmultilineeq@label}
% Within the current multiline equation, we patch the double backslash macro
% (for more details, see https://tex.stackexchange.com/a/59117/18401).
\ifundef{\original@local@double@backslash}{%
\global\let\original@local@double@backslash\\%
\global\let\\\patched@double@backslash%
}{}
}
% We define a hack to be applied at the end of each multiline equation
% environment (currently, only `align(*)' and `multline(*)').
\def\endhack{%
% We globally unpatch the double backslash macro
\global\let\\\original@double@backslash%
\global\undef\original@local@double@backslash
}
\makeatother
\appto\align{\beginhack}
\csappto{align*}{\beginhack}
\appto\endalign{\endhack}
%
\appto\multline{\beginhack}
\csappto{multline*}{\beginhack}
\appto\endmultline{\endhack}
\begin{document}
Foo\footnote{\tiny\lipsum[1]}
\begin{multline}
x = abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\[1cm]
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz \\
+ abcdefghijklmopqrstuvwyz
\end{multline}
Foo\\Bar.
\begin{tabular}{l}
Foo\\Bar.
\end{tabular}
\begin{figure}[b]
\centering
\includegraphics[height=1cm]{example-image-a}
\caption{A nice figure}
\label{nice-figure}
\end{figure}
\begin{align}
1 + 1 & = 2 \\
2 + 1 & = 3 \\
3 + 1 & = 4 \\
4 + 1 & = 5 \\
5 + 1 & = 6 \\
6 + 1 & = 7 \\
7 + 1 & = 8 \\
8 + 1 & = 9 \\
1 + 1 & = 2 \\
2 + 1 & = 3 \\
3 + 1 & = 4 \\
4 + 1 & = 5 \\
5 + 1 & = 6 \\
6 + 1 & = 7 \\
7 + 1 & = 8 \\
8 + 1 & = 9 \\
1 + 1 & = 2 \\
2 + 1 & = 3 \\
3 + 1 & = 4 \\
4 + 1 & = 5 \\
5 + 1 & = 6 \\
6 + 1 & = 7 \\
7 + 1 & = 8 \\
8 + 1 & = 9 \\
1 + 1 & = 2 \\
2 + 1 & = 3 \\
3 + 1 & = 4 \\
4 + 1 & = 5 \\
5 + 1 & = 6 \\
6 + 1 & = 7 \\
7 + 1 & = 8 \\
8 + 1 & = 9 \\
9 + 1 & = 10
\end{align}
\end{document}