# The biblatex has problems with \par having \prevdepth

Russian paragraphs have not too short last lines as the \Arussian substitution for \par does. But this approach creates conflicts with biblatex package. Is there any method to make it run?

Here is a short example of the problem:

\documentclass{article}

\usepackage{biblatex}

\let\origpar\par

% Donald Arseneau, [in:]
% Peter Wilson, Glisterings
% TUGboat, Volume 28 (2007), No. 2
\def\Arussianpar{\ifhmode \unskip
\discretionary{}%
{\hbox{\hskip2\parindent
\vrule depth 273sp
width 0sp height \ht\strutbox}}%
{\hbox{\hskip\parindent}}%
\hskip-2\parindent minus 2\parindent
\hskip\hsize minus\hsize
\kern0pt\parfillskip0pt
\origpar
\ifdim\prevdepth=273sp
\nobreak
\vskip-2\baselineskip
\hbox{\strut}%
\fi
\fi}

\let\par\Arussianpar

\begin{document}
x
\end{document}


The pdflatex crashes with:

! Improper \prevdepth.
\par ...arfillskip 0pt \origpar \ifdim \prevdepth
=273sp \nobreak \vskip -2\...

-

You get the errors when reading english.lbx, that is before starting to typeset the document.

You should be able to solve the issue by writing

\AtBeginDocument{\def\par{\Arussianpar}}


\let\par\Arussianpar

However there are many situations in LaTeX where \par is (locally) redefined, so you don't necessarily get the desired paragraph breaks in all cases.