Code: Select all
\documentclass{article}
\begin{document}
a\footnote{b\par c}
% I tried to redefine \@footnotetext as it seems to be defined already from
% \show\@footnotetext ; but it I must have done something wrong, for
% afterwards, I cannot use \par within a footnote.
\makeatletter
\def\@footnotetext#1{\insert \footins {\reset@font \footnotesize
\interlinepenalty \interfootnotelinepenalty \splittopskip \footnotesep
\splitmaxdepth \dp \strutbox \floatingpenalty \@MM \hsize \columnwidth
\@parboxrestore \protected@edef \@currentlabel {\csname p@footnote\endcsname
\@thefnmark }\color@begingroup \@makefntext {\rule \z@ \footnotesep
\ignorespaces #1\@finalstrut \strutbox }\color@endgroup }}
\makeatother
a\footnote{b\par c}
\end{document}
PS Where are basic LaTeX commands defined?