config.tex

% === Config ===
\let\oldproofname=\proofname
\renewcommand{\proofname}{\color{red}{\rm\bf{\oldproofname}}}

\newenvironment{solution}
{\begin{proof}[\color{red}{$\mathbf{Solution}$}]}
	{\end{proof}}

\newenvironment{sketch}
{\begin{proof}[$\mathbf{Sketch}$]}
	{\end{proof}}

\newenvironment{answer}
{\begin{proof}[\color{purple}{$\mathbf{Answer}$}]\renewcommand{\qedsymbol}{}}
	{\end{proof}}

\renewcommand{\dateseparator}{/}
\renewcommand{\qedsymbol}{$\blacksquare$}
\newcommand\parallelogram{
  \mathord{\text{
    \tikz[baseline]
      \draw (0,.1ex) -- (.8em,.1ex) -- (1em,1.6ex) -- (.2em,1.6ex) -- cycle;}}}
% === -------------------- ===

% === DeclareMathOperator ===
\DeclareMathOperator{\rank}{rank}
\DeclareMathOperator{\nullity}{nullity}
\DeclareMathOperator{\spann}{span}
\DeclareMathOperator{\trace}{tr}
\DeclareMathOperator{\ii}{\mathrm{i}}
% === ------------------- ===