math-modesymbols
I was looking for a \equiv symbol, but with dots on the bottom, on each side of it. I looked up on the comprehensive LaTeX symbol list and couldn't find it.
I tried to write .\equiv ., but didn't like the result and, unfortunately, I don't know exactly what the symbol stands for, my guess is something topology related.
Below, I leave an image on what the symbol look like, any help would be appreciated.
Thanks!
The MnSymbol package provides it.
\documentclass{article}
\usepackage{MnSymbol}
\begin{document}
So a rational map f: $V_1 \dashedrightarrow V_2$ is not a map at all;
\end{document}
There are some issues to consider:
The standard line width in TeX is 0.4pt, it is hardcoded in TeX as 26214sp.
\overline uses a different line width. It is taken from font parameter 8 of math font family 3 in TeX.
The standard math fonts (Computer Modern) are using 0.39998pt in all font sizes. But it is scalable in other fonts, e.g. package mathptmx with 10pt as class option:
0.3999pt in \textfont (\textstyle/\displaystyle)0.29591pt in \scriptfont (\scriptstyle)0.23993pt in \scriptscriptfont (\scriptscriptstyle)\overlineTeX constructs a \overline{...} the following way with θ as line width (pseudo code):
\vbox{
\kern θ
\hrule height θ
\kern 3*θ
\hbox{$...$}
}
Especially there is white space above the rule. This is useful, if the overlined symbol is put in the denominator of a fraction, for instance.
TeX uses cramped math style for the math expression of \overline. This means, the superscripts are moved down a little, for a better visual appearance.
Thus \overline looks like a good choice for the "house" symbols. However, the vertical lines should use the same line width as used by \overline.
TeX inserts 3 * θ (θ = line width of \overline) between the formula and the line in \overline. This cannot be easily changed without loosing cramped style. (AFAIK only LuaTeX can set cramped style explicitly.)
Extra space is added above the line in \overline, see above.
Usually symbols have side bearings, space at the left and right side of the symbol. The exact amount is usually not available in TeX. The example uses 2 * θ as horizontal space between the vertical lines and the formula. Also a horizontal space 1.5 * θ is put outside the vertical lines. Some kind of side bearings of the new symbol to avoid touching of housed math expressions.
Since the OP wants longer lines (see comment), the example adds 2 * θ as additional depth. (3 * θ seems too large, because there is not a underline that needs some distance from the formula.)
The full example also takes into account the different math styles, thus macro \house respects the current math sizes.
\documentclass{article}
\usepackage{mathptmx}
\makeatletter
\newcommand*{\house}[1]{%
\mathord{%
\mathpalette\@house{#1}%
}%
}
\newcommand*{\@house}[2]{%
% #1: math style
% #2: expression that gets the "house"
% get the line width of `\overline' in the current math font size
\dimen@=\fontdimen8 %
\ifx#1\scriptscriptstyle\scriptscriptfont
\else\ifx#1\scriptstyle\scriptfont
\else\textfont\fi\fi
3 %
\sbox0{%
$#1%
\vrule width\dimen@\relax
\overline{%
\kern2\dimen@
\begingroup % to keep changes of \dimen@ in #2 local
#2%
\endgroup
\kern2\dimen@
}%
\vrule width\dimen@\relax
\mathsurround=1.5\dimen@ % outside margin
$%
}%
% TeX adds an empty space above `\overline', it needs to be
% removed to get the correct height for the `\vrule's
\ht0=\dimexpr\ht0-\dimen@\relax
\dp0=\dimexpr\dp0+2\dimen@\relax
\vbox{%
\kern\dimen@ % reinsert previously removed space
\copy0 %
}%
}
\begin{document}
\[
\textstyle % same size as \displaystyle
\house{\alpha + \beta}
\stackrel{\mbox{\tiny T}}{=}
\house{\alpha} + \house{\beta}^n
\]
\[
\scriptstyle
\house{\alpha + \beta}
\stackrel{\mbox{\tiny S}}{=}
\house{\alpha} + \house{\beta}^n
\]
\[
\scriptscriptstyle
\house{\alpha + \beta}
\stackrel{\mbox{\tiny SS}}{=}
\house{\alpha} + \house{\beta}^n
\]
\[
\def\x{\frac{\house{\alpha + \beta}}{\house{\alpha} + \house{\beta}}}
\x, \frac{\x}{\x}
\]
\[
\underbrace{\overline{\alpha^2}, \house{\alpha^2}}_{\mbox{\tiny cramped}} \ne
\overline{\mbox{$\alpha^2$}}, \house{\mbox{$\alpha^2$}}
\]
\end{document}
Best Answer
I guess you want a relation symbol:
The braces around
\equivmake it into an ordinary symbol, so TeX doesn't add space around it, but it will around the whole construction that's declared\mathrel.