Math & Science ⇒ Variables under \forall symbol?

[joachim]

First of all: hi out there!

I googled it and searched the forum, but did not find an answer:
My problem is that I would like to display quantified variables under the quantifier symbol (\forall, \exists) rather than next to it, where it can easily be confused with the quantified term in certain cases. Is there any possibility to do this?

What I'm looking for would be a command similar to \sum_{i \in I}{...}

Thanks in advance,
Joachim

[localghost]

You will have to use a notation called »Quantification« [1]. These operator symbols behave exactly like those for integrals and sums. See the sample below.

Code: Select all

\documentclass[11pt,a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}

\begin{document}
  \begin{align*}
    \bigwedge_{\varepsilon>0}&\quad\bigvee_{\delta>0} \\
    \intertext{Is equivalent to}
    \forall\varepsilon>0&\quad\exists\delta>0
  \end{align*}
\end{document}

[1] Quantification - Wikipedia, the free encyclopedia


Best regards and welcome to the board
Thorsten

[frabjous]

A possibly easier way would just be to use \mathop from amsmath, which makes any arbitrary argument behave like \int, etc:

Code: Select all

\documentclass{article}
\usepackage{amsmath}

\begin{document}

$\displaystyle\mathop{\forall}_{x>5} (Fx \rightarrow Gx)$

\end{document}

Though I personally think that's a very odd looking notation for quantification.

An improvement might be to use \mathlarger from relsize for a larger quantifier:

Code: Select all

\documentclass{article}
\usepackage{amsmath,relsize}

\begin{document}

$\displaystyle\mathop{\mathlarger{\mathlarger{\mathlarger{\forall}}}}_{x>5} (Fx \rightarrow Gx)$

\end{document}

Shorten with a custom command.

[joachim]

Thank you both for your help!
That's exactly what I was looking for.