# Copying \subsection style to \subsubsection

\documentclass[a4paper,twoside, symmetric,justified,notoc, nobib]{tufte-book}

\titleclass{\subsubsection}{straight}

\begin{document}

\frontmatter
\pagenumbering{roman}
\setcounter{secnumdepth}{-1}

\mainmatter

\section{CHAPTER 1}
\subsection{Introduction}

\end{document}


Using the tufte-book class, I've been trying to define \subsubheading as I'm finding that \subheading alone isn't giving me enough flexibility for nesting content.

I found this question here on tex.SE which appears to want a similar thing, but in my case I'm not interested in the additional formatting (I don't wish to define the formatting from scratch, but rather just inherit formatting).

My aim is to just copy the formatting for \subsection and use this for \subsubsection.

My solution to this was to define a new titleclass such that \titleclass{\subsubsection}{straight} (this was suggested in several other posts and is covered in the LaTeX companion as away of introducing new sections/titles), but what I can't do is make it format correctly. Whilst in the ToC everything looks fine, on the page, the {straight} command gives bold, upright text.

Is there a way of making this new title class inherit the style of the old \subsection?

• So, basically, you want subsubsection-level headers to use a regular-weight (non-bold) italic font -- is this right? Please advise. – Mico Sep 3 '17 at 17:32
• Yes. Well, more specifically to use the exact formatting of \subsection (such that if I ever decided to change \subsection, \subsubsection would also inherit those changes (though if the only way of doing it is to make them look the same, that would be fine for the time being). – NotEvans. Sep 3 '17 at 17:35

\documentclass[a4paper,twoside, symmetric,justified,notoc, nobib]{tufte-book}
\titleclass{\subsubsection}{straight}
\titleformat{\subsubsection}%
[hang]% shape
{\normalfont\large\itshape}% format applied to label+text
{\thesubsubsection}% label
{1em}% horizontal separation between label and title body
{}% before the title body
[]% after the title body

\begin{document}
[...]

• Thanks, seems to do the job! Weirdly though, the numbering has changed relative to just having \titleclass{\subsubsection}{straight} - its now just x.x.x instead of x.x.x.x as it was previously (but its still fine in the t.o.c as x.x.x.x) – NotEvans. Sep 3 '17 at 17:56
• Ah, the label should be \thesubsubsection see my edited answer – user2478 Sep 3 '17 at 18:07
• Thanks! I think the subsubsections will look better if you remove the \large from the font definition, as it will distinguish them from subsections. – Júda Ronén Mar 1 at 13:35