Newlines after section headings in amsart

Question

This latex code:

\documentclass[9pt]{amsart}

\begin{document}
  \subsubsection*{Animals}
  Rabbit horse monkey cow
\end{document}

Generates something that looks approximately like this:

Animals. Rabbit horse monkey cow.

I'd like to add a newline after the section heading, but if I use \\ with

\subsubsection*{Animals}\

I get:

! LaTeX Error: There's no line here to end.

If I put the \\ inside the brackets, with Animals, then I get a newline but it separates "Animals" from the period:

Animals

. Rabbit horse monkey cow.

How can I put a newline after the section heading without separating it from the period?

EDIT: A good solution is provided below using redefinition of \subsubsection, but a simpler method is to do

\subsubsection*{Animals}\hspace*{\fill} \\
Rabbit horse monkey cow.

Answer 1

You can redefine \subsubsection appropriately; here's the original definition in amsart.cls

\def\subsubsection{\@startsection{subsubsection}{3}%
  \z@{.5\linespacing\@plus.7\linespacing}{-.5em}%
  {\normalfont\itshape}}

and you can redefine it using something like this:

\documentclass[9pt]{amsart}
\usepackage[parfill]{parskip}    

\makeatletter
\def\subsubsection{\@startsection{subsubsection}{3}%
  \z@{.5\linespacing\@plus.7\linespacing}{.1\linespacing}%
  {\normalfont\itshape}}
\makeatother

\begin{document}
\subsubsection*{Animals}
Rabbit horse monkey cow
\end{document}

Another option, not requiring knowing the inner definition of \subsubsection, is to use the titlesec package:

\documentclass[9pt]{amsart}
\usepackage[parfill]{parskip}
\usepackage{titlesec}

\titleformat{\subsubsection}
  {\normalfont\normalsize\itshape}{\thesubsubsection}{1em}{}
\titlespacing*{\subsubsection}{0pt}{3.25ex plus 1ex minus .2ex}{0ex plus .2ex}

\begin{document}
\subsubsection*{Animals}
Rabbit horse monkey cow
\end{document}

However, if you are writing a paper for a submission to an AMS journal, pay attention to the following warning from barbara beeton regarding the use of titlesec with the AMS document classes:

i can't recommend titlesec because it's an option we don't permit when a paper is submitted to an ams journal, so we've never tested it. (for the same reason, i can't "unrecommend" it either. for whatever it's worth, it has never been identified as causing failures with amsart; just "not tested here".)

Answer 2

A simple workaround not requiring any modification.

If you directly put \\ then it tells you there is no line here to end, but if you put any character before \\ it will allow you to create a new line.

So my workaround is put a ~ right after the \subsubsection{tittle}, and \\ after ~, the ~ create an invisible space after your title, and which enables you to create a new line for your visible paragraphs.

Answer 3

The simplest way would be to give subsubsection some invisible text before the newline:

subsubsection*{Animals}~\\Rabbit horse monkey cow

You may choose \mbox{} instead of ~.

Answer 4

You could simply add \hfill at the end of the \subsubsection{} like so

\subsubsection{Something}\hfill

Answer 5

If you want to fine tune the spacing after the linebreak then you can use an invisible rule e.g. \subsection{Animals}\rule[-10pt]{0pt}{10pt}\\