脚注：对相同的脚注文本保留相同的脚注编号（在所有文档中）

Question

这是解决方案。（它有很多检查，因为它也接受自定义数字，并且如果已经给出了特定的脚注文本，则更新旧数字）：

\documentclass{article}
\usepackage{lipsum}
\usepackage{pgffor}
\usepackage{xcolor}

\newcounter{myfootnote}

\let\oldfootnote=\footnote

\makeatletter
\def\footnote{\let\curfootnum\undefined\@ifnextchar[%
{\@ReadOptional}{\@ReadMandatory}}
\def\@ReadOptional[#1]{\def\curfootnum{#1}\@ReadMandatory}%
\def\@ReadMandatory#1{\xdef\curfoottext{#1}%
\ifnum\themyfootnote>0%
  \xdef\Found{0}%
  \foreach \n in {1,...,\themyfootnote}%
    {\expandafter\ifx\csname FootText\n\endcsname\curfoottext%
       \xdef\temppage{\csname FootLastPage\n\endcsname}%
       \xdef\tempnum{\n}%\ifx\curfootnum\undefined\n\else\curfootnum\fi
       \xdef\Found{1}%
     \fi%
     }%
  \ifnum\Found=0%
    \let\nextavail\undefined%
    \foreach \f in {1,...,\themyfootnote}%
    {\xdef\FoundNum{0}%
    \foreach \l in {1,...,\themyfootnote}%
    {\expandafter\ifnum\csname FootLastNumber\l\endcsname=\f%
    \xdef\FoundNum{1}%
    \breakforeach%
    \fi}%
    \ifnum\FoundNum=0%
    \xdef\nextavail{\f}%
    \fi%
    }%
    \refstepcounter{myfootnote}%
    \ifx\nextavail\undefined%
    \xdef\nextavail{\themyfootnote}%
    \fi%
    \xdef\tempn{\ifx\curfootnum\undefined\nextavail\else\curfootnum\fi}%
    \global\expandafter\let\csname FootLastNumber\themyfootnote\endcsname\tempn%
    \xdef\myp{\thepage}%
    \global\expandafter\let\csname FootLastPage\themyfootnote\endcsname\myp%
    \global\expandafter\let\csname FootText\themyfootnote\endcsname\curfoottext
    \oldfootnote[\csname FootLastNumber\themyfootnote\endcsname]{\curfoottext}%
  \else%
     \ifnum\thepage=\temppage%
         \ifx\curfootnum\undefined%
         \footnotemark[\csname FootLastNumber\tempnum\endcsname]%
         \else%
         \xdef\myp{\thepage}%
         \global\expandafter\let\csname FootLastPage\tempnum\endcsname\myp%
         \global\expandafter\let\csname FootLastNumber\tempnum\endcsname\curfootnum%
         \refstepcounter{myfootnote}%
         \global\expandafter\let\csname FootLastNumber\themyfootnote\endcsname\tempnum%
         \oldfootnote[\csname FootLastNumber\tempnum\endcsname]{\curfoottext}%
         \fi%
     \else%
         \ifx\curfootnum\undefined%
         \oldfootnote[\csname FootLastNumber\tempnum\endcsname]{\curfoottext}%
         \else%
         \global\expandafter\let\csname FootLastNumber\tempnum\endcsname\curfootnum%
         \oldfootnote[\csname FootLastNumber\tempnum\endcsname]{\curfoottext}%
         \refstepcounter{myfootnote}%
         \global\expandafter\let\csname FootLastNumber\themyfootnote\endcsname\tempnum%
         \fi%
         \xdef\myp{\thepage}%
         \global\expandafter\let\csname FootLastPage\tempnum\endcsname\myp%
     \fi%
  \fi%
\else%
  \refstepcounter{myfootnote}\global\expandafter\let\csname FootText\themyfootnote\endcsname\curfoottext%
  \xdef\temp{\thepage}%
  \global\expandafter\let\csname FootLastPage\themyfootnote\endcsname\temp%
  \xdef\temp{\ifx\curfootnum\undefined\themyfootnote\else\curfootnum\fi}%
  \global\expandafter\let\csname FootLastNumber\themyfootnote\endcsname\temp%
  \oldfootnote[\csname FootLastNumber\themyfootnote\endcsname]{\curfoottext}%
\fi}%
\makeatother


\begin{document}
\lipsum[1]
{\color{red}test1\footnote{test}}
\lipsum[1]
{\color{red}test2 same as 1\footnote{test}}
\lipsum[2]
{\color{red}test3 different\footnote{test2}}
\lipsum[1-3]
{\color{red}test4 same as 1 different page\footnote{test}}
\lipsum[1-2]
\lipsum[1-3]
{\color{red}test5 same as 2 different page\footnote{test2}}
\lipsum[1-3]
{\color{red}custom numbered\footnote[5]{custom numbered 5}}
\lipsum[1]
{\color{red} repeat custon numbered same page\footnote{custom numbered 5}}
\lipsum[1-5]
{\color{red} repeat custon numbered other page\footnote{custom numbered 5}}
\lipsum[1-3]
{\color{red}Again second\footnote{test2}}
\lipsum[1]{\color{red}A new one\footnote{test new}}
{\color{red}Another one double\footnote{test new two}\footnote{test new two}}
{\color{red}This has to be 6\footnote{test new three}}
{\color{red}From now 6 will forced to be 8\footnote[8]{test new three}}
\lipsum[1-2]
{\color{red} This footnote has to be 7\footnote{new text}}
\lipsum[1-2]
{\color{red} Repeating 8 to see if last number kept\footnote{test new three}}
\lipsum[1-2]
{\color{red} Custom updating footnote 2\footnote[2]{test new last}}\lipsum[3]
{\color{red} Repeating 2 to see if text "test new last" kept\footnote{test new last}}
\lipsum[3]
{\color{red} And numbers continues from 9\footnote{test new 9}}


\end{document}

这个想法是为了跟踪文本、最后一个数字（脚注标记）和每个脚注的最后一页。

如果您发现脚注中有已定义的文本，则将保留旧编号，除非您通过更新它\footnote[<new number>]{old text}。在最后一种情况下，将为以下相同的脚注保留给定的编号，但不会释放旧编号。

如果在同一页中发现两个相同的脚注，则页脚中只会打印一个。

如果您使用自定义编号定义脚注\footnote[<custom number>]{some text}，那么该编号将不适用于下一个脚注，除非您更改它。

输出：

第 1 页：

第2页：

第 4 页：

第 6 页：

第 7 页：

Answer 1