\lmoustache and \rmoustache manifesting as weird cropped "tails"

Question

I was just working on my LaTeX skills so I don't forget, so I went on this site and started replicating the most complex stuff I found. At first I thought it would be a piece of cake, but then I wrote this code and was absolutely perplexed.

\documentclass{article}

\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{fullpage}
\usepackage{commath}

\begin{document}

\[
\iiiint \limits_{\mathcal{Q}} f(w,x,y,z) \; \mathrm{d}w \; \mathrm{d}x \; \mathrm{d}y \; \mathrm{d}z \leq \oint_{\partial Q} f' \left( \max \left\{ \frac{\norm{w}}{|w^2 + x^2|} ; \frac{\norm{z}}{|y^2 + z^2|} ; \frac{\norm{w \oplus z}}{\norm{x \oplus y}} \right\} \right) \precapprox \biguplus_{\mathbb{Q} \Subset \bar{Q}} \left[ f^* \left( \frac{\lmoustache \mathbb{Q}(t)\rmoustache}{\sqrt{1 - t^2}} \right) \right]^{t=9}_{t=\alpha}
\]

\end{document}

At the first glance everything seems normal, but if you carefully look inspect the end of the line (the part with Q(t)) you figure out that the \lmoustache and \rmoustache are cropped out, disfigured. Here is a picture supporting my description.

I removed all of the non-vital packages so I made sure there was no redefinition issue or a clash of packages. Then, I tried to check if it wasn't an encoding problem by scaling \lmoustache and \rmoustache down with \scalebox. The result was the same, just a smaller "tail". So I am curious how to slove this problem and make my compilation identical to that included in the cited site.

Thank you in advance.

Answer 1

You can import the delimiters from another font family, I chose stix.

I also add some improvements, particularly \diff for the differential and omitting commath.

\documentclass{article}

\usepackage{amsmath,mathtools}
\usepackage{amssymb}
\usepackage{fullpage}

%% moustaches from STIX
\let\lmoustache\relax \let\rmoustache\relax
\DeclareFontEncoding{LS2}{}{}
\DeclareFontSubstitution{LS2}{stix}{m}{n}
\DeclareSymbolFont{stixlargesymbols}{LS2}{stixex}{m}{n}
\SetSymbolFont{stixlargesymbols}{bold}{LS2}{stixex}{b}{n}
\DeclareMathDelimiter{\lmoustache}{\mathopen} {stixlargesymbols}{"E6}{stixlargesymbols}{"EC}
\DeclareMathDelimiter{\rmoustache}{\mathclose}{stixlargesymbols}{"E7}{stixlargesymbols}{"ED}

%% \abs and \norm
\DeclarePairedDelimiter{\abs}{\lvert}{\rvert}
\DeclarePairedDelimiter{\norm}{\lVert}{\rVert}

%% differential
\newcommand{\diff}{\mathop{}\!\mathrm{d}}

\begin{document}

\begin{equation*}
\begin{aligned}
\iiiint_{\mathcal{Q}} f(w,x,y,z) \diff w \diff x \diff y \diff z 
&\leq 
\oint_{\partial Q} f'
  \left(
    \max \left\{ \frac{\norm{w}}{\abs{w^2 + x^2}} ; 
    \frac{\norm{z}}{\abs{y^2 + z^2}} ;
    \frac{\norm{w \oplus z}}{\norm{x \oplus y}} \right\}
  \right)
\\
&\precapprox
\biguplus_{\mathbb{Q} \Subset \bar{Q}}
  \left[ f^* \left(
    \frac{\lmoustache \mathbb{Q}(t)\rmoustache}{\sqrt{1 - t^2}}
  \right) \right]^{t=9}_{t=\alpha}
\end{aligned}
\end{equation*}

\begin{equation*}
\left\lmoustache\frac{a}{b}\right\rmoustache
\end{equation*}

\end{document}

About not using commath, see

https://tex.stackexchange.com/a/135985/4427

https://tex.stackexchange.com/a/123408/4427

https://tex.stackexchange.com/a/265987/4427

https://tex.stackexchange.com/a/325341/4427

https://tex.stackexchange.com/a/297273/4427

https://tex.stackexchange.com/a/89470/4427

Answer 2

the moustache are not really fully defined symbols they are just re-constructed bits of large braces, so are only available in large sizes, not normal size.

\documentclass{article}

\usepackage{amsmath}

\begin{document}

\[
\lmoustache Q \rmoustache
\left\lmoustache Q \right\rmoustache
\]

\end{document}