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The not equal symbol (), has its slash from the upper-right to the bottom-left. For example:

\begin{equation}
    i  \neq  j
\end{equation}

Typesets the following:

i ≠ j

How can I obtain a similar symbol, whose slash directionality is reversed (i.e., from the upper-left to the bottom-right, as displayed below)?

A non-canonical 'not equal' symbol, with its slash directionality reversed, as described above.

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3 Answers 3

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You could make use of \reflectbox (as has been pointed out in the comments), but it won't be usable in super- or subscripts:

\documentclass{article}
\usepackage{graphicx}

\newcommand{\flipneq}{\mathrel{\reflectbox{$\neq$}}}

\begin{document}
$A \flipneq B \neq C$
\end{document}

enter image description here

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  • 2
    \newcommand{\flipneq}{\mathrel{\mathpalette\flipneq@\relax}} and \newcommand{\flipneq@}[2]{\reflectbox{$\m@th#1{\neq}$}} (requires the usual \makeatletter and \makeatother.
    – egreg
    Commented Dec 14, 2021 at 15:19
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You can construct this in a similar manner to the methods described in a related question.

For example, adapting a prior answer and enhanced via another, you can do the following:

\documentclass{article}

\usepackage{amssymb}
\usepackage{amsmath}

\makeatletter
\newcommand{\rneq}{\mathrel{\vphantom{\neq}\mathpalette\do@rneq\relax}}

\newcommand{\do@rneq}[2]{%
  \ooalign{%
    $#1\m@th=$\cr
    \hidewidth$#1\m@th\backslash$\hidewidth\cr
  }%
}
\makeatother

\begin{document}
    \Huge

    \begin{align*}
        i   &   \neq j\\
        \\
        i   &   \rneq j\\
        \\
        \\
        i   &   \neq_{a} j\\
        \\
        i   &   \rneq_{a} j\\
    \end{align*}
\end{document}

This yields:

Compiled output of above: depicts i ≠ j, and then a line below with the same but the direction of the slash reversed; then a double line break, followed by the same two lines, except with both symbols having a sub-scripted 'a'

This has the advantage of working fine with most kerning and sub/super-scripting (as shown), and allowing easy adjustment, by changing the spacing within the \rneq command.

You also can view this example on Overleaf.

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You can define a \flipnot symbol that can be used like \not:

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

\makeatletter
\newcommand{\flipnot}{\mathrel{\mathpalette\flipnot@\relax}}
\newcommand{\flipnot@}[2]{%
  \begingroup
  \sbox\z@{$#1\not$}%
  \raisebox{\dimexpr\depth-\dp\z@}{\scalebox{1}[-1]{$\m@th#1\not$}}%
  \endgroup
}
\makeatother
\newcommand{\fneq}{\flipnot=} % \neq is \not=

\begin{document}

$\neq\fneq$

$a\neq b\fneq c^{\fneq}$

\end{document}

enter image description here

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