How do you write the equal-to symbol with delta on top ("delta-equal to")? One similar to http://www.decodeunicode.org/de/u+225c. Are special packages required for that?
It is supposed to be used for definition of equalities, similar to :=.
[Tex/LaTex] Delta-equal to symbol
relation-symbolssymbols
Related Solutions
You can overlay the symbols the following way: Box the wider one and let the other one lap over it (using \rlap or \llap). The correct centering is achieved by placing the second character into a box with the equal width but using \hss to center it. The correct size for the different math modes can be adjusted using \mathchoice.
\documentclass{article}
\def\qeq{\mathrel{%
\mathchoice{\QEQ}{\QEQ}{\scriptsize\QEQ}{\tiny\QEQ}%
}}
\def\QEQ{{%
\setbox0\hbox{=}%
\rlap{\hbox to \wd0{\hss?\hss}}\box0
}}
\textwidth=2cm
\begin{document}
$ A \qeq B $
$ A = B $
\[ A \qeq B \]
\[ A = B \]
$ S_{ A \qeq B } $
$ S_{ A = B } $
$ S_{S_{ A \qeq B }} $
$ S_{S_{ A = B }} $
\end{document}
Result
Just use Heiko Oberdiek's centernot package:
\documentclass{article}
\usepackage{centernot}
\usepackage{amsmath}
\begin{document}
$a\centernot\ll b \centernot\Delta c$
$a\centernot\longrightarrow b$
$a\centernot{\xrightarrow{1234567}} b$
\end{document}
Best Answer
How about
\triangleqfrom the AMS fonts? Loading\usepackage{amssymb}will make the command available