math-modestacking-symbolssyntax
There are posts here explained how to Add a comment on top of "equal" and "approximate" symbols , the idea is to use \stackrel{text}{=}, however, if the text is a bit long, for example I'd like to right
LHS\stackrel{t=x^n}{=}RHS
then the text over the equal symbol is a bit too long.
How could I make it more pretty?
To negate the \perp (perpendicular) symbol, the command \not\perp provides a simple solution, but this negated symbol doesn't look that great IMHO:
If you load the mathabx package, you get the command \notperp which looks pretty good, as does now the output of \not\perp. The same effect can be achieved if you load either the MnSymbol package or the fdsymbol package and use the command \notperp (same name used by both packages). Notice, though, that even if you load the MnSymbol of the fdsymbol package, the output of \not\perp still looks pretty bad, i.e., as bad as if you hadn't loaded any extra package at all.
Addendum: Following a request by the OP, here's an MWE that shows how to load the mathabx package and generate the symbol using the package's \notperp macro, as well as with \not\perp"
\documentclass{article}
\usepackage{mathabx}
\begin{document}
$a \notperp b$, $c \not\perp d$
\end{document}
Next, here's an MWE that shows the use of the MnSymbol package to generate these symbols:
\documentclass{article}
\usepackage{MnSymbol}
\begin{document}
$a \nperp b$, $c \not\perp d$
\end{document}
Finally, with the use of the fdsymbol package and its \nperp macro:
\documentclass{article}
\usepackage{fdsymbol}
\begin{document}
$a \nperp b$, $c \not\perp d$
\end{document}
Happy TeXing!
You can use a combination of \stackrel and \mathclap (from the mathtools package):
\documentclass{article}
\usepackage{mathtools}
\newcommand\myeq{\stackrel{\mathclap{\normalfont\mbox{def}}}{=}}
\begin{document}
\begin{align*}
a &\myeq b \\
&=c \\
&= d.
\end{align*}
\end{document}
If using mathtools is not an option, you can use a \makebox of width 0pt:
\documentclass{article}
\usepackage{amsmath}
\newcommand\myeq{\mathrel{\stackrel{\makebox[0pt]{\mbox{\normalfont\tiny def}}}{=}}}
\begin{document}
\begin{align*}
a &\myeq b \\
&=c \\
&= d.
\end{align*}
\end{document}
Even better, if amsmath has been loaded, is to use \overset instead of \stackrel; a little example using \tiny\sffamily for "def" :
\documentclass{article}
\usepackage{amsmath}
\newcommand\myeq{\mathrel{\overset{\makebox[0pt]{\mbox{\normalfont\tiny\sffamily def}}}{=}}}
\begin{document}
\begin{align*}
a &\myeq b \\
&=c \\
&= d.
\end{align*}
\end{document}
Inside the argument for \mbox one can use some of the font modifiers, as I did in my second and third examples.
Particularly, I don't like this kind of notation (it's not really necessary); you should consider if you really need the text above the equal sign.
Best Answer
Prettiest of all ;-)