3

In one of the slides at my university the negation of \forall was used. It looked like this:

I want to use the symbol, so I searched for it using this StackExchange post, but I couldn't find it anywhere.

Is it even used? If yes, what's the LaTeX command?

cwallenwein
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  • 6
    You'd say that there exists an x for which not F. – JPi Nov 30 '19 at 12:42
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    I've never seen it. You may do \usepackage{centernot} and \centernot{\forall}. – egreg Nov 30 '19 at 12:46
  • From a purely mathematical perspective, I would say it is never used – Alexandre Khoury Nov 30 '19 at 23:53
  • I've never seen it used in symbolic logic either. You'd say not for-all and not not-for-all. @JPi is wrong about the equivalence, though. The exists not version is only equivalent if a non-empty domain is assumed, which it is not in all systems. – cfr Dec 01 '19 at 00:58

3 Answers3

5

I've never seen it. Anyway:

\documentclass{article}

\newcommand{\nforall}{%
  \ooalign{$\forall$\cr\hidewidth$\!/$\hidewidth\cr}%
}

\begin{document}

\[
\nforall x\in A : F
\]

\[
\lnot\forall x\in A : F
\]

\end{document}

enter image description here

egreg
  • 1,121,712
3

My humble proposal, as alternative, it is to use cancel package. enter image description here

%% Compile and read me!
\documentclass[a4paper,12pt]{article}
\usepackage{amsmath,amssymb}
\usepackage{cancel}
\begin{document}
${\cancel \forall} x\in A : F$
\end{document}
Sebastiano
  • 54,118
3

Others seem to be complicating this.

\documentclass{article}
\begin{document}
$\not \forall x \in A: F$
\end{document}

enter image description here

Phelype Oleinik
  • 70,814
Eric Towers
  • 131
  • Welcome to TeX.SX! To add the picture you just drag and drop on the text box. I added it for you. – Phelype Oleinik Dec 01 '19 at 00:17
  • @PhelypeOleinik : I generate PDFs and DVIs. The input textbox rejects both. The insert an image dialog does not accept PDFs or DVIs. So I don't know what you are dragging and dropping, but it doesn't appear to be an output type I generate. – Eric Towers Dec 01 '19 at 00:21
  • Oh, now I understand. Yes, it only accepts image files. I convert the PDF to PNG using ImageMagick. If you use Linux, that's convert -trim -density 300 file.pdf output.png (-trim trims white space, -density 300 is a good enough value for posting pictures here). But of course you can just take a screenshot of the PDF and post that as well. – Phelype Oleinik Dec 01 '19 at 00:28