# Looking for a specific symbol used in set theory, can't find on detexify

I'm looking for a specific symbol for typesetting my lecture notes in logic and set theory.

The character is used to define a new set from two existing sets alpha and beta (which are ordinals):

In the above image, the \bot character is not what I want: instead of one vertical line I would like two parallel ones. Detexify found \coprod and \amalg (upside down product signs), which are close, but ideally the symbol that I'm looking for should be sans-serif.

In other words, I would like a symbol that is to \bot what \vDash is to \vdash. Unfortunately, I do not know the name of the operation that this symbol is representing, so meaning-based googling is ruled out.

-
Look for \newcommand\independent in the list of symbols. On the other hand, it seems \amalg to me. –  egreg Mar 7 '14 at 23:43
Very helpful thank you, the independent tip enabled me to find a solution (if you post that as an answer I can mark this question closed, or alternatively I can post the answer myself). Although I appreciate that you are probably sick of newbies posting questions asking for specific symbols in this forum, none of the tips listed in your link would have helped me to find the answer, as I seemingly encountered this symbol out of its usual context, and detexify didn't turn anything up. –  DCopperfield Mar 7 '14 at 23:54

In the Comprehensive List (texdoc symbols) one can find something near to what you want, looking for \independent. Here's a modified version:

\documentclass{article}

\makeatletter
\DeclareRobustCommand{\varamalg}{%
\mathbin{\mathpalette\var@malg\perp}%
}

\newcommand\var@malg[2]{%
\rlap{$\m@th#1#2$}\mkern6mu{#1#2}%
}
\makeatother

\begin{document}
$\alpha\varamalg\beta=\alpha\times\{0\}\cup\beta\times\{1\}$
\end{document}


Adjust \mkern6mu to suit.

-
Exactly what I needed, thanks. –  DCopperfield Mar 8 '14 at 0:05
I'm a bit of a newbie; what's the reason behind using the @ symbol in your \newcommand def instead of a? –  at least three characters Mar 8 '14 at 16:08
@user2615799 A different name must be used for the auxiliary macro; changing an a into @ is traditional. Observe that \makeatletter before the code was necessary. –  egreg Mar 8 '14 at 16:23

I'm not sure of the exact aspect of what you require, but would not \upmodelsor \upVdashbelow be what you want? According to the name of the first symbol, it should be of use in model theory. These come from mdsymbol (math symbols for Myriad Pro), and the same exist in MnSymbol (mat symbols for Minion Pro).

-
\upmodels is spot on what I wanted. Nice find, what a shame that these didn't turn up on Detexify! Thank you for your answer. –  DCopperfield Mar 8 '14 at 0:13
@DCopperfield Note that loading mdsymbol changes all math symbols. –  egreg Mar 8 '14 at 0:54
@egreg: That's right. But cannot individual symbols in that font be loaded through a \DeclareMathSymbol, or something like that? I'm not very familiar with this. –  Bernard Mar 8 '14 at 1:01
@Bernard Yes, see Importing a Single Symbol From a Different Font –  egreg Mar 8 '14 at 1:04

Yet another solution (adjust -8mu to your needs)

\documentclass{article}
\usepackage{amsmath}

\newcommand{\dbot}{\mathbin{\text{$\bot\mkern-8mu\bot$}}}

\begin{document}

$\alpha\dbot\beta=\alpha\times\{0\}\cup\beta\times\{1\}$

$A \dbot B_{A \dbot B_{A \dbot B}}$

\end{document}


-