Anonymous 5071
Continuing http://tex.stackexchange.com/questions/678909 , for all the theorem-like environments in our document, we wish to have a little bit more horizontal space (than the default space) separating the head of the environment (whether it is fully automatically generated or also contains a user-given part) from its contents. To this end, we tried to redefine \@thmcounterend ([thx to @DavidCarlisle](http://tex.stackexchange.com/questions/678909#comment1684992_678928)):


\documentclass{svmono}% v5.10 (2021/09/08) from https://www.springer.com/gp/authors-editors/book-authors-editors/your-publication-journey/manuscript-preparation#toc-49268 or directly from https://resource-cms.springernature.com/springer-cms/rest/v1/content/20566/data/monographs
\overfullrule=1mm
\pagestyle{empty}
\begin{document}%
\newcommand{\test}[1]{
\noindent Remark with a short name:
\begin{remark}[Short remark name]
Text of a remark with a short name.
\end{remark}
Remark without a special name:
\begin{remark}
Text of an unnamed remark.
\end{remark}
Remark with a line-filling, long name and a label:
\begin{remark}[Long remark name. More words. More words. More words. Mo\ldots]\label{#1}
Text of a remark with a long name.
\end{remark}
}%
\section*{Originally}
\test{RemarkLabelOne}
\section*{With \texttt{\textbackslash @thmcounterend} being a simple space}
\makeatletter\def\@thmcounterend{ }\makeatother
\test{RemarkLabelTwo}
\section*{With \texttt{\textbackslash @thmcounterend} redefining the simple space}
\makeatletter\def\@thmcounterend{\def\ {\hspace{2\fontdimen2\font plus2\fontdimen3\font minus2\fontdimen4\font}}}\makeatother
\test{RemarkLabelThree}
\end{document}


Running pdflatex on this results in

![mwe.png](/image?hash=e82af8ecf03e9d9745d390cee9f7d207c84b4eb073d985e589ab6ae7c2ef5e85)

As we see, the original version is simply bad: the title and the contents are separated by a too small space (cf. Remark 2). If we redefine \@thmcounterend to be a simple space, an unwanted white line may emerge (cf. Remark 6).  If we redefine \@thmcounterend to redefine the space to be of the double length, but the user does not supply a title, then the horizontal space after the remark number is still small as originally (cf. Remark 8).  Any help on how to make more horizontal space between the remark title and the remark body even if there's no user parameter supplying the title?

Crossposts: http://latex.org/forum/viewtopic.php?f=4&t=35426&p=118775 , https://texwelt.de/fragen/29112 , http://golatex.de/viewtopic.php?f=4&t=25006&p=121236 , and http://tex.stackexchange.com/questions/678941 .
Skillmon
We can probe in which of the two contexts the \@thmcounterend is used by checking whether it's followed by the control space. If that's the case we input your double-spaced control space redefinition (without actually redefining it) and remove the control space, else we simply add a space (combining the two solutions). The overfull box in the following example is because of the counter being 12 (so wider than 9).


\documentclass{svmono}% v5.10 (2021/09/08) from https://www.springer.com/gp/authors-editors/book-authors-editors/your-publication-journey/manuscript-preparation#toc-49268 or directly from https://resource-cms.springernature.com/springer-cms/rest/v1/content/20566/data/monographs
\overfullrule=1mm
\pagestyle{empty}

\newcommand\macroname{\texttt{\textbackslash @thmcounterend}}

\begin{document}%
\newcommand{\test}[1]{
\noindent Remark with a short name:
\begin{remark}[Short remark name]
Text of a remark with a short name.
\end{remark}
Remark without a special name:
\begin{remark}
Text of an unnamed remark.
\end{remark}
Remark with a line-filling, long name and a label:
\begin{remark}[Long remark name. More words. More words. More words. Mo\ldots]\label{#1}
Text of a remark with a long name.
\end{remark}
}%
\section*{Originally}
\test{RemarkLabelOne}
\section*{With \macroname\ being a simple space}
\makeatletter\def\@thmcounterend{ }\makeatother
\test{RemarkLabelTwo}
\section*{With \macroname\ redefining the simple space}
\makeatletter\def\@thmcounterend{\def\ {\hspace{2\fontdimen2\font plus2\fontdimen3\font minus2\fontdimen4\font}}}\makeatother
\test{RemarkLabelThree}
\section*{With some overconvoluted definition of \macroname}
\makeatletter
\def\@thmcounterend{\@ifnextchar\ {\hspace{2\fontdimen2\font plus2\fontdimen3\font minus2\fontdimen4\font}\@gobble}{ }}
\makeatother
\test{RemarkLabelFour}
\end{document}


![remarksandtheirspace.png](/image?hash=ee3b6ab142b45b9904f8115b2a7822c57c3936710caa523f8a782e211866749f)

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