How to negate \rhd

Question

Is there a good way to represent the negation of \rhd?. I have tried something like \not\rhd, but it does not look nice. Looking around I haven't found any good suggestion.

Answer 1

You shouldn't use \rhd as a relation symbol, because it's a binary operation symbol. You can find it in latexsym (deprecated) or amsfonts:

  \DeclareMathSymbol{\lhd}     {\mathbin}{AMSa}{"43}
  \DeclareMathSymbol{\unlhd}   {\mathbin}{AMSa}{"45}
  \DeclareMathSymbol{\rhd}     {\mathbin}{AMSa}{"42}
  \DeclareMathSymbol{\unrhd}   {\mathbin}{AMSa}{"44}

The same symbols used as relation symbols are called differently:

\ams@DeclareMathSymbol{\vartriangleright} {\mathrel}{AMSa}{"42}
\ams@DeclareMathSymbol{\vartriangleleft}  {\mathrel}{AMSa}{"43}
\ams@DeclareMathSymbol{\trianglerighteq}  {\mathrel}{AMSa}{"44}
\ams@DeclareMathSymbol{\trianglelefteq}   {\mathrel}{AMSa}{"45}

and amssymb (that loads amsfonts) has

\DeclareMathSymbol{\ntrianglerighteq}{\mathrel}{AMSb}{"34}
\DeclareMathSymbol{\ntrianglelefteq}{\mathrel}{AMSb}{"35}
\DeclareMathSymbol{\ntriangleleft}  {\mathrel}{AMSb}{"36}
\DeclareMathSymbol{\ntriangleright} {\mathrel}{AMSb}{"37}

So the answer is to load amssymb and to use \ntriangleright.

\documentclass{article}
\usepackage{amssymb}
\begin{document}
$x\ntriangleright y$
\end{document}