Tweaking theorem style last parameter traps?

Question

When I modified the \newtheoremstyle last parameter to get a list for a listoftheorems new command I want to define later, I got some unpleasant side effects I want to get rid of.

First unwanted side effect a blank space between the period and the theorem body or number appears !

Second unwanted side effect the period after the lemma name (which is in normal font when there is one) appears in bold not in normal font when there is an optional name for the lemma. And I want it to be in bold when there is no name.

Third unwanted side effect the name of the theorem is no more in normal font but get the same font than Theorem word (here, in small cap). I do not want this.

What should I do? Below is a MWE

\documentclass{amsbook}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{etoolbox}

\newtheoremstyle{mytheorem}
{6pt plus 0pt minus 2pt}
{0pt plus 0pt minus 2pt}
{\slshape}
{}{\scshape}
{.}
{5pt plus 1pt minus 1pt}
{\thmname{#1}\thmnumber{ #2}\thmnote{ (#3)}
     \ifstrempty{#3}%
      {\addcontentsline{def}{subsection}{#1~\thethm}}%
      {\addcontentsline{def}{subsection}{#1~\thethm~(#3)}}}

\newtheoremstyle{mylemma}
{6pt plus 0pt minus 2pt}
{0pt plus 0pt minus 2pt}
{\slshape}
{}
{\bfseries}
{.}
{5pt plus 1pt minus 1pt}
{}

\theoremstyle{mytheorem}
\newtheorem{thm}{Theorem}
\theoremstyle{mylemma}
\newtheorem{lem}{Lemma}

\begin{document}
\begin{thm}
Bad effect
\end{thm}
\begin{thm}[Wrong2]
Double Bad effect
\end{thm}
\begin{lem}[Wrong4]
Bad effect
\end{lem}
\begin{lem}
Good
\end{lem}
\end{document}

Answer 1

You just have an unprotected end-of-line. The other effects can be cured by adding appropriately \normalfont.

\documentclass{amsbook}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}

\makeatletter
\newtheoremstyle{mytheorem}
{6pt plus 0pt minus 2pt}
{0pt plus 0pt minus 2pt}
{\slshape}
{}{\scshape}
{.}
{5pt plus 1pt minus 1pt}
{\thmname{#1}\thmnumber{ #2}\thmnote{\normalfont\ (#3)}%
 \addcontentsline{def}{subsection}{#1\string~#2\@ifempty{#3}{}{\string~(#3)}}%
}
\makeatother


\newtheoremstyle{mylemma}
{6pt plus 0pt minus 2pt}
{0pt plus 0pt minus 2pt}
{\slshape}
{}
{\bfseries}
{.}
{5pt plus 1pt minus 1pt}
{\thmname{#1}\thmnumber{ #2}\thmnote{\normalfont\ (#3)}}

\theoremstyle{mytheorem}
\newtheorem{thm}{Theorem}
\theoremstyle{mylemma}
\newtheorem{lem}{Lemma}

\begin{document}
\begin{thm}
Bad effect
\end{thm}
\begin{thm}[Wrong2]
Double Bad effect
\end{thm}
\begin{lem}[Wrong4]
Bad effect
\end{lem}
\begin{lem}
Good
\end{lem}
\end{document}

I used \@ifempty that amsthm defines for these cases.

However, I would never use boldface for lemmas and small caps for theorems: too much difference.

Note also usage of #2 instead of \thethm: it stands for the current statement number, so it works independently of the counter's name.

Here are the entries in the .aux file:

\@writefile{def}{\contentsline {subsection}{Theorem~1}{1}}
\@writefile{def}{\contentsline {subsection}{Theorem~2~(Wrong2)}{1}}

Answer 2

here is a modified example, nearly the same as the original, except with % signs following all the non-final lines of the \newtheoremstyle definitions, and a more comprehensive styling in the last line of the mylemma style; although overkill, it's the easiest way to get around the "bold period" problem.

also shown is the equivalent material in default style for amsbook.

\documentclass{amsbook}
\usepackage{etoolbox}

\newtheoremstyle{mytheorem}%
{6pt plus 0pt minus 2pt}%
{0pt plus 0pt minus 2pt}%
{\slshape}%
{}{\scshape}%
{.}%
{5pt plus 1pt minus 1pt}%
{\thmname{#1}\thmnumber{ #2}\thmnote{ \normalfont (#3)}%
     \ifstrempty{#3}%
      {\addcontentsline{def}{subsection}{#1~\thethm}}%
      {\addcontentsline{def}{subsection}{#1~\thethm~(#3)}}}

\newtheoremstyle{mylemma}%
{6pt plus 0pt minus 2pt}%
{0pt plus 0pt minus 2pt}%
{\slshape}%
{}%
{\bfseries}%
{.}%
{5pt plus 1pt minus 1pt}%
{\thmname{#1}\thmnumber{ #2}\thmnote{ \normalfont (#3)}}

\theoremstyle{mytheorem}
\newtheorem{thm}{Theorem}
\theoremstyle{mylemma}
\newtheorem{lem}{Lemma}

\theoremstyle{plain}
\newtheorem{pthm}{Theorem}
\newtheorem{plem}{Lemma}

\begin{document}
\begin{thm}
Bad effect
\end{thm}
\begin{thm}[Wrong2]
Double Bad effect
\end{thm}
\begin{lem}[Wrong4]
Bad effect
\end{lem}
\begin{lem}
Good
\end{lem}

\begin{pthm}
Bad effect
\end{pthm}
\begin{pthm}[Wrong2]
Double Bad effect
\end{pthm}
\begin{plem}[Wrong4]
Bad effect
\end{plem}
\begin{plem}
Good
\end{plem}

\end{document}

Answer 3

You can move some of the commands in to the then or else parts of the test of the third argument #3.

\documentclass{amsbook}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{etoolbox}

\newtheoremstyle{mytheorem}
{6pt plus 0pt minus 2pt}
{0pt plus 0pt minus 2pt}
{\slshape}
{}{\scshape}
{.}
{5pt plus 1pt minus 1pt}
{\textnormal{\bfseries \thmname{#1}\thmnumber{ #2}}%
     \ifstrempty{#3}%
      {\addcontentsline{def}{subsection}{#1~\thethm}}%
      {\thmnote{ (#3)}\addcontentsline{def}{subsection}{#1~\thethm~(#3)}}}

\newtheoremstyle{mylemma}
{6pt plus 0pt minus 2pt}
{0pt plus 0pt minus 2pt}
{\slshape}
{}
{\bfseries}
{}
{5pt plus 1pt minus 1pt}
{\thmname{#1}\thmnumber{ #2}%
  \ifstrempty{#3}{.}{\textnormal{\thmnote{ (#3).}}}}

\theoremstyle{mytheorem}
\newtheorem{thm}{Theorem}
\theoremstyle{mylemma}
\newtheorem{lem}{Lemma}

\begin{document}

\begin{thm}
First version.
\end{thm}

\begin{thm}[Attribution]
Another version.
\end{thm}

\begin{lem}[Atrribution]
Example.
\end{lem}

\begin{lem}
Good.
\end{lem}

\end{document}