A solution with TikZ:
\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\newlength\thetawidth
\newlength\thetaheight
\newcommand*{\SquareTheta}{%
\begingroup
\setlength{\mathsurround}{0pt}%
\settowidth{\thetawidth}{$\Theta$}%
\settoheight{\thetaheight}{$\Theta$}%
\begin{tikzpicture}[
x=\thetawidth,
y=\thetaheight,
]
\draw[line width=.1\thetawidth, line cap=round]
(0.125,.05\thetawidth) -- +($(0,1)-(0,.1\thetawidth)$)
(0.875,.05\thetawidth) -- +($(0,1)-(0,.1\thetawidth)$);
\draw[line width=.05\thetaheight, line cap=butt]
(0.125,.025\thetaheight) -- +(0.75,0)
($(0.125,1)-(0,.025\thetaheight)$) -- +(0.75,0);
\draw[line width=.1\thetawidth, line cap=butt]
(0.275,0.5) -- (0.725,0.5);
\draw[line width=.0375\thetaheight, line cap=butt]
($(0.275,0.5)-(0,.1\thetawidth)$) -- +(0,.2\thetawidth)
($(0.725,0.5)-(0,.1\thetawidth)$) -- +(0,.2\thetawidth);
\end{tikzpicture}%
\endgroup
}
\begin{document}
\renewcommand*{\arraystretch}{0}
\begin{tabular}{c}
$\Theta$ \\[1pt]
$\SquareTheta$ \\[1pt]
$\Theta\SquareTheta$
\end{tabular}
\end{document}
First case: square dot with equal spaceing
The first case is probably \centerdot
of package amssymb
:
\documentclass{article}
\usepackage{amssymb}
\begin{document}
\[
\exists n \in \mathbb{N} \centerdot \forall m \in \mathbb{N} \centerdot m < n
\]
\let\oldcenterdot\centerdot
\renewcommand*{\centerdot}{\mathrel{\oldcenterdot}}%
\[
\exists\,n \in \mathbb{N} \centerdot \forall\,m \in \mathbb{N} \centerdot m < n
\]
\end{document}
\centerdot
is a binary operator. In the image in the question, the spacing seems to be slightly larger. Therefore the second line uses
- the spacing of a relational operator by redefining
\centerdot
and
- adds a thin space after the quantifiers.
Second case: round dot with asymmetrical spacing
In the second case a bold version of the dot could be used. The spacing seems to be a little special, the example uses
- half of a thin space at the left and
- a thick space at the right (as for relational operators).
\documentclass{article}
\usepackage{amsmath,amssymb}
\newcommand*{\anddot}{%
\mathclose{}%
\nonscript\mskip.5\thinmuskip
\boldsymbol{.}%
\;%
\mathopen{}%
}
\begin{document}
\[
\forall x \in \mathbb{R} \anddot x^2 \ge 0
\]
\end{document}
Best Answer
You need the mathabx package:
For such things I highly recommend trying:
texdoc symbols
Code:
Edit: just to complete, here is a print screen from the documentation cited.