preamble.sty

\RequirePackage[T1]{fontenc}
\RequirePackage{verbatim}
\RequirePackage[table]{xcolor}
\RequirePackage[svgnames]{xcolor}
\RequirePackage{colortbl}
\definecolor{myblue}{rgb}{0.0,0.2,0.4}%
\colorlet{themecolor}{myblue}
\RequirePackage{enumitem}
\setlist*[enumerate,1]{labelindent=0pt,label={(\alph*)}}
\RequirePackage{setspace}
\RequirePackage[singlelinecheck=false]{caption}
\RequirePackage{xurl}
\RequirePackage[pdfpagelabels,
            colorlinks = true,
            linkcolor = black,
            urlcolor  = myblue,
            citecolor = black,
            anchorcolor = black]{hyperref}
\RequirePackage{tabularray}
\UseTblrLibrary{booktabs}
\RequirePackage{booktabs, cellspace, multirow}
\RequirePackage{amssymb}% \nless, \square and \blacksquare
\RequirePackage{float}% option [H] to figure
\RequirePackage{array}% \newcolumntype macro
\newcolumntype{L}[1]{>{\raggedright\let\newline\\\arraybackslash\hspace{0pt}}m{#1}}
\newcolumntype{C}[1]{>{\centering\let\newline\\\arraybackslash\hspace{0pt}}m{#1}}
\newcolumntype{R}[1]{>{\raggedleft\let\newline\\\arraybackslash\hspace{0pt}}m{#1}}
\newcolumntype{Q}[1]{>{\vfil\hfil$}m{#1}<{$\hfill\vfill}} % centered, automatic math mode
\newcolumntype{X}{>{$}l<{$}}
\newcolumntype{Y}{>{$}c<{$}}
\newcolumntype{Z}{>{$}r<{$}}
\newcolumntype{M}{Z@{${}={}$}X}% align around the equality sign | uses X and Z above
\RequirePackage{amsfonts}
\RequirePackage{fontawesome5}% useful symbols
\RequirePackage[fleqn]{amsmath}
\RequirePackage{bm}% \boldsymbol
\setlength\parindent{0pt}% no indents
%\setlength{\parskip}{0.75\baselineskip plus 2pt}% control space between paragraphs
\RequirePackage[parfill]{parskip}% no indents, lineskip
\RequirePackage{scalerel}% \scaleleftright[1.75ex]{<}
\RequirePackage{nccmath}% fleqn environment, medium-sized fraction \mfrac

\RequirePackage{mathtools}%\DeclarePairedDelimiter, etc.

% degree symbol
% \newcommand*{\degree}{\textup{°}}% suddenly stopped working
\usepackage{gensymb}% substitute for the above

% radian symbol
\newcommand{\radian}{\,\textrm{rad}}

% set notation
\renewcommand{\emptyset}{\varnothing}% empty set
\newcommand{\intersect}{\cap}% intersection
\newcommand{\union}{\cup}% union
\newcommand{\ci}{\perp\!\!\!\perp}% conditional independence

% number sets
\newcommand{\N}{\ensuremath{\mathbb{N}} }% set of natural numbers
\newcommand{\Z}{\ensuremath{\mathbb{Z}} }% set of integers
\newcommand{\Q}{\ensuremath{\mathbb{Q}} }% set of rational numbers
\newcommand{\R}{\ensuremath{\mathbb{R}} }% set of real numbers
\newcommand{\Cx}{\ensuremath{\mathbb{C}} }% set of complex numbers
\let\Natural\N
\let\Integer\Z
\let\Rational\Q
\let\Real\R
\let\Complex\Cx

% better notation for sets
\let\union\cup
\let\Union\bigcup
\let\inter\cap
\let\Inter\bigcap

% mathematical symbols
\newcommand{\e}{\mathrm{e}}% exponential
\newcommand{\diff}{\mathop{}\!\mathrm{d}}% differential symbol
\DeclareMathOperator{\sign}{\mathrm{sign}}% sign
\DeclareMathOperator*{\argmax}{argmax}
\DeclareMathOperator*{\argmin}{argmin}
\DeclareMathOperator*{\freq}{freq}% freq
\DeclareMathOperator*{\indep}{\perp \!\!\! \perp}% independence symbol
\DeclareMathOperator{\trace}{Tr}

% statistical symbols
\DeclareMathOperator{\PROB}{\mathbb{P}}% probability
\DeclareMathOperator{\EXP}{\mathbb{E}}% expectation
\DeclareMathOperator{\VAR}{\mathbb{V}}% variance
\DeclareMathOperator{\COV}{\mathbb{C}}% covariance
\DeclareMathOperator{\SE}{\mathrm{SE}}% standard error
\DeclareMathOperator{\SD}{\mathrm{SD}}% standard deviation
\DeclareMathOperator{\MSE}{\mathrm{MSE}}% mean squared error

% trigonometric operators
\DeclareMathOperator{\arcsec}{arcsec}
\DeclareMathOperator{\arccot}{arccot}
\DeclareMathOperator{\arccsc}{arccsc}

% floor/ceiling
\DeclarePairedDelimiter\ceil{\lceil}{\rceil}
\DeclarePairedDelimiter\floor{\lfloor}{\rfloor}

% auto-scaling parentheses
\DeclarePairedDelimiter{\parens}{(}{)}

% auto-scaling brackets
\DeclarePairedDelimiter{\bracks}{[}{]}


% absolute value
\DeclarePairedDelimiter\abs{\lvert}{\rvert}

% mathematical norm
\DeclarePairedDelimiter\norm{\lVert}{\rVert}

% placeholder
\newcommand*{\placeholder}{\makebox[1ex]{\textbf{$\cdot$}}}

% tighter modulo command
\newcommand{\modulo}[1]{\;(\mathrm{mod}\,#1)}

% Smaller binomial command
\newcommand{\binomial}[3][0.8]{\scalebox{#1}{$\dbinom{#2}{#3}$}}

% smaller multiplication symbol
\DeclareMathOperator{\mult}{\mbox{\scriptsize$\times$}}

% right slash
\newcommand{\rslash}{\raisebox{.15ex}{/}}

% bold+underline command
\newcommand\underbold[1]{\underline{\bfseries\boldmath#1}}

% displaystyle commands
\newcommand*{\Sum}{\displaystyle\sum}
\newcommand*{\Prod}{\displaystyle\prod}
\newcommand*{\Frac}[2]{\displaystyle\frac{#1}{#2}}
\newcommand*{\Int}{\displaystyle\int}
\newcommand*{\Sqrt}[1]{\displaystyle\sqrt{#1}}
\newcommand*{\Binom}[1]{\displaystyle\binom{#1}}

% command \sfrac for small fractions | alternative to package xfrac
\newcommand{\sfrac}[2]{\scalebox{0.65}{\ensuremath{\left.#1\middle/#2\right.}}}

% Permutations/Combinations
\newcommand*{\permcomb}[4][0mu]{{{}^{#3}\mkern#1#2_{#4}}}
\newcommand*{\perm}[1][-3mu]{\permcomb[#1]{P}}
\newcommand*{\comb}[1][-1mu]{\permcomb[#1]{C}}

% Arrangements / Derangements
\newcommand*{\arr}[1][-1mu]{\,\permcomb[#1]{A}}% arrangements
\newcommand*{\arrange}[2]{A_{#1,#2}} 
\newcommand*{\derange}[3][0mu]{{\mkern#1#2_{#3}}}

% multiset | double-parenthesis notation
\newcommand{\multiset}[2]{\bigl(\!{\binom{#1}{#2}}\!\bigr)}
\newcommand{\Multiset}[2]{\left(\!\!{\displaystyle\binom{#1}{#2}}\!\!\right)}

%% define commands for ticking in or crossing out
\RequirePackage{amssymb}
\RequirePackage{pifont}
\newcommand{\cmark}{\mbox{\ding{51}}}
\newcommand{\xmark}{\mbox{\ding{55}}}

% crossing-out digits
\newcommand{\crossout}[2][1]{%
  \vphantom{\rslash}%
  {\ooalign{\hidewidth$\crosses{#1}$\hidewidth\cr$#2$\cr}}%
}
\newcommand{\crosses}[1]{%
  \ifcase#1\relax
    \or
    \rslash\or
    \rslash\mskip-5.5mu\rslash\or
    \rslash\mskip-5.5mu\rslash\mskip-5.5mu\rslash%
  \fi
}

% Triangle and Arc/Sector hat symbols
%\RequirePackage{amsmath}% already loaded
\DeclareSymbolFont{yhlargesymbols}{OMX}{yhex}{m}{n}
\DeclareMathAccent{\trianglehat}{\mathord}{yhlargesymbols}{"E6}
\DeclareMathAccent{\sectorhat}{\mathord}{yhlargesymbols}{"F3}

% minipagex correctly applies paragraph skip preferences
\newlength{\currentparskip}
\newlength{\currentparindent}
\newenvironment{minipagex}[2][]
  {\setlength{\currentparskip}{\parskip}% save the value
    \setlength{\currentparindent}{\parindent}%
   \begin{minipage}[#1]{#2}% open the minipage
   \setlength{\parskip}{\currentparskip}% restore the value
   \setlength{\parindent}{\currentparindent}% restore the value
  }
  {\end{minipage}}

% load tikz and libraries
\RequirePackage{tikz}
\usetikzlibrary{intersections}
\usetikzlibrary{positioning}
\usetikzlibrary{angles}
\usetikzlibrary{quotes}
\usetikzlibrary{arrows.meta}
\usetikzlibrary{decorations.markings, decorations.text}
\usetikzlibrary{shapes,shapes.misc}
\usetikzlibrary{backgrounds}

\newcommand{\tikzmark}[1]{\tikz[baseline={(#1.base)},remember picture] \node[draw=red,thick,circle,inner sep=0.5pt,minimum width=3ex] (#1) {$#1$};}
\tikzset{connect/.style={
    red,in=225,out=315,thick}}

% load pgfplots and library for coordinate system 
\RequirePackage{pgfplots}
\pgfplotsset{compat=newest}% use bleeding edge version: risky
\usetikzlibrary{arrows.meta}

% text box with tikz, to use inside a node
\tikzstyle{textbox} = [draw=blue!80!black, fill=blue!1!white, very thick,
    rectangle, rounded corners, inner sep=10pt, inner ysep=20pt]


% angled brackets to use as an option to \begin{cases} \end{cases}
% does not stretch if linespacing is increased
\makeatletter
\renewenvironment{cases}[1][\lbrace]{%
  \def\@ldelim{#1}
  \matrix@check\cases\env@cases
}{%
  \endarray\right.%
}
\patchcmd{\env@cases}{\lbrace}{\@ldelim}{}{}
\makeatother


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Set Graphics Paths
\RequirePackage{graphicx}
%\graphicspath{}% initialize the graphicspath, no longer needed with new version
\DeclareGraphicsExtensions{.pdf,.png,.jpg,.jpeg}%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% append paths to the existing graphicspath
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% https://tex.stackexchange.com/questions/171587/
% usage: \appendtographicspath{{a}{b}{c}}
\ExplSyntaxOn
\NewDocumentCommand{\appendtographicspath}{m}
 {
  \tl_if_exist:cF { Ginput@path } { \tl_new:c { Ginput@path } }
  \clist_map_function:nN { #1 } \steven_gpath_append:n
 }
\cs_new_protected:Nn \steven_gpath_append:n
 {
  \tl_gput_right:cn { Ginput@path } { {#1} }
 }
% for debugging
\NewDocumentCommand{\showgraphicspath}{}{\tl_show:c { Ginput@path }}
\ExplSyntaxOff
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% append path to existing paths for input files
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% https://tex.stackexchange.com/questions/79058/
\makeatletter
\newcommand\appendtoinputpath[1]{%
  \providecommand*{\input@path}{}%
  \edef\input@path{#1\input@path}% prepend new path to path list
}
\makeatother
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% ENVIRONMENTS
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Proof | based on theorem environment
\RequirePackage{amssymb}% required
%\RequirePackage{amsthm}% ntheorem and amsthm not compatible
\newcommand*{\qed}{\null\nobreak\hfill\ensuremath{\square}}% \qed already defined by amsthm
\RequirePackage[thmmarks,amsthm]{ntheorem}
\theoremheaderfont{\bfseries}
\theorembodyfont{\normalfont}
\theoremseparator{:}
%\theoremsymbol{$\blacksquare$}
%\newtheorem*{theorem}{Theorem}% already defined
\newtheorem*{definition}{Definition}
%\newtheorem*{proof}{Proof}% already defined
\AtEndEnvironment{proof}{\hfill$\blacksquare$}

%% Question/Solution | based on tcolorbox
% solution | show/hide toggle
\RequirePackage{etoolbox}\newtoggle{showSolution}\togglefalse{showSolution}%
\ifsolution
  \toggletrue{showSolution}% default is false
\fi

% math box with empheq+tcolorbox
\RequirePackage{empheq}
\RequirePackage[many]{tcolorbox}
\newtcbox{\mathbox}[1][]{%
    nobeforeafter, math upper, tcbox raise base, enhanced, sharp corners, colframe=black, colback=white, boxrule=1pt, #1}
\newtcbox{\alignbox}[1][]{%
    nobeforeafter, math upper, tcbox raise base, enhanced, colframe=black, colback=white, boxrule=1pt, #1}
% usage: \begin{solution}[Optional title]
\tcbset{onecolummnstyle/.style={
  breakable,
  enhanced,
  lower separated=false,
  text width=\linewidth,
  %colframe=themecolor,
  coltext=themecolor,
  frame hidden,
  colback=white,
  sharp corners,
  attach boxed title to top left={yshift=0ex,xshift=5pt},% negative xshift
  boxed title style={
    colframe=white,
    colback=white,
    sharp corners,
    },
  overlay={
      \draw[themecolor!80!white, line width=1.5pt] (frame.north west)--(frame.south west);
  },
  %fonttitle=\sffamily
  fonttitle={\normalsize\itshape\bfseries\color{themecolor}}
  }
}
\newtcolorbox[auto counter]{question}[1][]{
  title={Question},
  onecolummnstyle,
  #1
}
% conditionally define solution environment
% omit solution if \ifsolution is False
\iftoggle{showSolution}{
  \newtcolorbox[auto counter]{solution}[1][]{
    title={Solution},
    onecolummnstyle,
    #1
  }
}{%
    %\RequirePackage{verbatim}% already loaded
    \newenvironment{solution}{\vspace{0em}\expandafter\comment}{\expandafter\endcomment} 
}%

% box inside a box
\usepackage{varwidth}
\newtcolorbox{boxinbox}[2][]{
        enhanced,
        colback=gray!10!white,
        boxrule=0.1pt,
        colframe=themecolor,
        fonttitle=\bfseries,
        %center title,
        width=\linewidth,
        nobeforeafter,
        %lifted shadow={1mm}{-2mm}{3mm}{0.1mm}{black!50!white},
        title={#2},
        #1
    }
% answer environment | redundant with solution | somewhat earlier version
\RequirePackage{etoolbox}\newtoggle{showAnswers}\togglefalse{showAnswers}%
\ifanswer
  \toggletrue{showAnswers}% default is false
\fi
\ifsolution% added to accommodate both answer and solution environments
  \toggletrue{showAnswers}% default is false
\fi
% define answer environment
\iftoggle{showAnswers}{
    \newtcolorbox{answer}{%
      breakable, 
      enhanced, 
      width=\linewidth,
      parbox=false, % normal paragraph spacing
      colback=blue!2!white,
      opacityback=0.5,enhanced jigsaw,
      colframe=blue!80!black
    }
    %\newenvironment{answer}{\vspace{1em}}{}
}{%
    %\RequirePackage{verbatim}% already loaded
    \newenvironment{answer}{\vspace{0em}\expandafter\comment}{\expandafter\endcomment} 
}%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%