LaTeX2e <2017/01/01> patch level 3
Babel <3.9r> and hyphenation patterns for 83 language(s) loaded.
(/usr/local/texlive/2016/texmf-dist/tex/latex/base/book.cls
Document Class: book 2014/09/29 v1.4h Standard LaTeX document class
(/usr/local/texlive/2016/texmf-dist/tex/latex/base/bk12.clo
File: bk12.clo 2014/09/29 v1.4h Standard LaTeX file (size option)
)
\c@part=\count79
\c@chapter=\count80
\c@section=\count81
\c@subsection=\count82
\c@subsubsection=\count83
\c@paragraph=\count84
\c@subparagraph=\count85

 *File List*
    book.cls    2014/09/29 v1.4h Standard LaTeX document class
    bk12.clo    2014/09/29 v1.4h Standard LaTeX file (size option)
fontspec.sty    2017/02/12 v2.6 Font selection for XeLaTeX and LuaLaTeX
   expl3.sty    2017/02/10 v6878 L3 programming layer (loader)
expl3-code.tex    2017/02/10 v6878 L3 programming layer
l3xdvipdfmx.def
  xparse.sty    2017/02/10 v6878 L3 Experimental document command parser
fontspec-xetex.sty    2017/02/12 v2.6 Font selection for XeLaTeX and LuaLaTeX

\ExplSyntaxOn
\cs_if_exist:NF \__xparse_normalize_type_k:w
 {
  \cs_set_eq:NN \__xparse_normalize_type_k:w \__xparse_normalize_type_e:w
  \cs_set_eq:NN \__patchxparse_IfNoValueTF:n \IfNoValueTF
  \cs_generate_variant:Nn \__patchxparse_IfNoValueTF:n { f }
  \cs_set:Npn \IfNoValueTF #1 { \__patchxparse_IfNoValueTF:f { \tl_head:n { #1 } } }
 }
\ExplSyntaxOff

[paulo@cambridge ~] $ time vim

real	0m1.109s
user	0m0.420s
sys	0m0.036s
[paulo@cambridge ~] $ time emacs

real	0m17.413s
user	0m5.405s
sys	0m0.357s

\DeclareDocumentCommand\@quantity{ t\big t\Big t\bigg t\Bigg g o d() d|| }
{ % Flexible automatic bracketing of an expression in () or [] or {} or ||
	% Handles manual override of sizing
	\IfBooleanTF{#1}{\let\ltag\bigl \let\rtag\bigr}{
		\IfBooleanTF{#2}{\let\ltag\Bigl \let\rtag\Bigr}{
			\IfBooleanTF{#3}{\let\ltag\biggl \let\rtag\biggr}{
				\IfBooleanTF{#4}
				{\let\ltag\Biggl \let\rtag\Biggr}
				{\let\ltag\left \let\rtag\right}
			}
		}
	}
	% Handles actual bracketing
	\IfNoValueTF{#5}{
		\IfNoValueTF{#6}{

\DeclareDocumentCommand\@admat{mmggggggg}
{
	\newtoks\matrixtoks
	\global\matrixtoks = {}