math-operatorsstacking-symbolssymbols
I wondered how to create a symbol that looks like "#" (for connected sum) and "ff" for "fiber". The size and angles should be like the "#", but the vertical bars should look like two f`s. Another way to describe it would be a fortissimo symbol with two bars.
http://upload.wikimedia.org/wikipedia/commons/7/71/Music-fortissimo.png
Here's a solution that doesn't require the use of additional packages. The new command, \vertiii, takes one argument; the triple vertical bars resize automatically depending on the size of the argument. For the MWE below, I've actually set the spacing between the vertical bars to be slightly less than what's generated by \[l,r]Vert -- you can adjust the spacing to suit your taste by changing the value of the argument of the four \kern commands.
Addendum: I've modified the code -- by inserting curly braces around the entire command -- to allow for the use of the command \vertiii in subscripts and superscripts as well.
\documentclass{article}
\usepackage{amsmath,amssymb}
\newcommand{\vertiii}[1]{{\left\vert\kern-0.25ex\left\vert\kern-0.25ex\left\vert #1
\right\vert\kern-0.25ex\right\vert\kern-0.25ex\right\vert}}
\begin{document}
$\vertiii{a}$,
$\vertiii{\int_0^1 a(x)\,\mathrm{d}x}$,
$\displaystyle \vertiii{\int_0^1 a(x)\,\mathrm{d}x}_\vertiii{b}$
$\lVert a \rVert$ (for comparison)
$c_\vertiii{d}$, $f^\vertiii{g}$
\end{document}
Here's an implementation with \ooalign:
\documentclass{article}
\usepackage{amsmath}
\newcommand{\avsum}{\mathop{\mathpalette\avsuminner\relax}\displaylimits}
\makeatletter
\newcommand\avsuminner[2]{%
{\sbox0{$\m@th#1\sum$}%
\vphantom{\usebox0}%
\ooalign{%
\hidewidth
\smash{\vrule height\dimexpr\ht0+1pt\relax depth\dimexpr\dp0+1pt\relax}%
\hidewidth\cr
$\m@th#1\sum$\cr
}%
}%
}
\makeatother
\begin{document}
\[
\sum_{i=1}^{m} \avsum_{j=1}^{n} a_{ij}
\]
\[
\textstyle\sum_{i=1}^{m} \avsum_{j=1}^{n} a_{ij}
\]
\[
\scriptstyle\sum_{i=1}^{m} \avsum_{j=1}^{n} a_{ij}
\]
\[
\scriptscriptstyle\sum_{i=1}^{m} \avsum_{j=1}^{n} a_{ij}
\]
\end{document}
Best Answer
Here, I introduce
\varhashand\varfhashto be used in tandem (or for sans font,\sfvarhashand\sfvarfhash). I started with a\sffamilyfto build things from there. In the last line, I overlay the two glyphs to see if they compare.Since I use the current font for the
f, this answer will depend on the font chosen for the document. Bu the answer can be tailored to suit.EDITED to provide both sans and roman versions.
And here is a version with
\intinstead off, which allows more flexibility with the placement of the horizontal bars: