How to create a custom negation symbol with double lines

Question

I'm trying to create a negation symbol with two upper lines, like this example I found in a paper (regular negation for comparison):

Detexify didn't know the symbol and I even looked through the comprehensive symbol list, but wasn't able to find anything. Any help on how to find/create this symbol would be greatly appreciated!

Answer 1

You can superimpose \neg to a clipped (and lowered) version thereof.

\documentclass{article}
\usepackage{trimclip}

\makeatletter
\newcommand{\dneg}{\mathord{\vphantom{\neg}\mathpalette\dneg@\relax}}
\newcommand{\dneg@}[2]{%
  \ooalign{%
    $\m@th#1\neg$\cr
    \raisebox{0.8\height}{\clipbox{0pt {0.6\height} 0pt 0pt}{$\m@th#1\neg$}}\cr
  }%
}
\makeatother

\begin{document}

$\neg\varphi$ $\dneg\varphi$

$\dneg\varphi\scriptstyle\dneg\varphi\scriptscriptstyle\dneg\varphi$

\Large
$\dneg\varphi\scriptstyle\dneg\varphi\scriptscriptstyle\dneg\varphi$

\end{document}

Answer 2

\documentclass{article}
\usepackage{amsmath}
\makeatletter
% based on https://tex.stackexchange.com/a/110981
\providecommand*{\dneg}{%
  \mathord{%
    \mathpalette\@dneg{}%
  }%
}
\newcommand*{\@dneg}[2]{%
  \ooalign{%
    $\m@th#1\neg$\cr
    \sbox0{$#1\neg$}%
    \dimen@=0.4\ht0%
    \hidewidth\raise\dimen@\box0\hidewidth
  }%
}
\makeatother
\begin{document}
\parindent0pt
$\neg$ $\dneg$\par
\bigskip
{\large $\neg$ $\dneg$}\par
\bigskip
{\Huge $\neg$ $\dneg$}\par
\end{document}

Edit: changed to \mathord, see comment by Bernard.

Answer 3

Just I add my proposal.

\documentclass[a4paper,12pt]{article}
\usepackage{amsmath,amssymb,stmaryrd}
\usepackage{graphicx}

\newcommand{\rrc}{\mathrel{\rotatebox{90}{$\rrfloor$}}}
\newcommand{\rfl}{\mathrel{\rotatebox{90}{$\rfloor$}}}
\begin{document}
$\rrc\varphi$; $\rfl \varphi$.
\end{document}