[Tex/LaTex] Typesetting d’Alembertian symbol

Question

I've seen that usually, the d'Alembertian is written using the command \Box, however, this displays a square with all sides identical. I would like to write it in this other way:

in which, the right and below sides are bolder, so that resembles more to the Laplacian symbol.

Answer 1

Build a square with thicker lines the same size of \square:

\documentclass{article}
\usepackage{amsmath,amssymb}

\makeatletter
\newcommand{\dalembertian}{\mathop{\mathpalette\dalembertian@\relax}}
\newcommand{\dalembertian@}[2]{%
  \begingroup
  \sbox\z@{$\m@th#1\square$}%
  \dimen0=\fontdimen8
    \ifx#1\displaystyle\textfont\else
    \ifx#1\textstyle\textfont\else
    \ifx#1\scriptstyle\scriptfont\else
    \scriptscriptfont\fi\fi\fi3
  \makebox[\wd\z@]{%
    \hbox to \ht\z@{%
      \vrule width \dimen0
      \kern-\dimen0
      \vbox to \ht\z@{
        \hrule height \dimen0 width \ht\z@
        \vss
        \hrule height 2\dimen0
      }%
      \kern-2.5\dimen0
      \vrule width 2.5\dimen0
    }%
  }%
  \endgroup
}
\makeatother

\begin{document}

$\dalembertian = \mathop{{}\Delta}-\partial_0^2$

$\scriptstyle\dalembertian = \mathop{{}\Delta}-\partial_0^2$

$\scriptscriptstyle\dalembertian = \mathop{{}\Delta}-\partial_0^2$

{\Large$\dalembertian = \mathop{{}\Delta}-\partial_0^2$}

\end{document}