How do I move the first line of every paragraph up with everypar and vspace?

Question

I'm trying to modify https://tex.stackexchange.com/a/399944/2066 to adjust the spacing after sections headings which are not immediately followed by other section headings. However, if I replace the \hrule\vspace{1ex} with \vspace{-\baselineskip} in that answer, using the code

\documentclass{article}
\usepackage{lipsum}
\makeatletter
\def\@afterheading{%
  \@nobreaktrue
  \everypar{%
    \if@nobreak
    \@nobreakfalse
    \clubpenalty \@M
    \if@afterindent \else
                    {\setbox\z@\lastbox
                      \vspace{-\baselineskip}%
                    }%
                    \fi
                    \else
                    \clubpenalty \@clubpenalty
                    \everypar{}%
                    \fi}}
\makeatother
\begin{document}
\section{Test}
\subsection{Sub Test}
\lipsum[4]
\subsection{Sub Test}
\lipsum[4]
\section{Test}
\subsection{Sub Test}
\lipsum[4]
\section{Test}
\lipsum[4]
\subsection{Sub Test}
\section[optional]{Test}
\subsection[optional]{Sub Test}
\lipsum[4]
\section{blblblb}
\lipsum[4]
\end{document}

I get the very ugly

How do I get the first line of the paragraph to be moved up, rather than the second line?

My experiments always used @afterindentfalse. Not sure what \if@afterindent was intended for. — John Kormylo, Jan 03 '21 at 21:56

score 2 · Accepted Answer · answered Jan 03 '21 at 21:39

You are adding the negative space after the first line of the paragraph, you need to back out of horizontal mode with \par to add the negative space before the first line, but then take account that the indentation suppression needs to be re-done for the "real" paragraph.

So this does what is intended although hooking into the after-indent test is only a very loose approximation to testing for a following section head so this will not work in all cases.

\documentclass{article}
\usepackage{lipsum}
\makeatletter
\def\@afterheading{%
  \@nobreaktrue
  \everypar{%
    \if@nobreak
    \@nobreakfalse
    \clubpenalty \@M
    \if@afterindent \else
                    {\setbox\z@\lastbox
                      \par\vspace{-\baselineskip}\noindent
                    }%
                    \fi
                    \else
                    \clubpenalty \@clubpenalty
                    \everypar{}%
                    \fi}}
\makeatother
\begin{document}
\section{Test}
\subsection{Sub Test}
\lipsum[4]
\subsection{Sub Test}
\lipsum[4]
\section{Test}
\subsection{Sub Test}
\lipsum[4]
\section{Test}
\lipsum[4]
\subsection{Sub Test}
\section[optional]{Test}
\subsection[optional]{Sub Test}
\lipsum[4]
\section{blblblb}
\lipsum[4]
\end{document}

Thanks! This is exactly what I wanted – Jason Gross Jan 03 '21 at 21:56 — Jason Gross, Jan 03 '21 at 21:56

How do I move the first line of every paragraph up with everypar and vspace?

1 Answers1