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I usually use \fint to denote normalized integration. I would like to produce the same slanted line across a double integral \iint. The command \fiint does not seem to exist. How can I get this notation for normalized double integrals?

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  • In contemporary mathematics, the use of double integrals is often considered to be old-fashioned. Aesthetically, it would be rather ugly, in my opinion.
    – Siminore
    Jul 16, 2016 at 15:39
  • Can you provide a pointer to \fint? I don't know what the symbol looks like, or what package provides it. Jul 18, 2016 at 10:25
  • 1
    the package ofr \fint is esint
    – user110191
    Jul 26, 2016 at 3:25

2 Answers 2

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Using amsmath, esint and graphicx packages, you can declare the \fiint math operator in your preample, as: \DeclareMathOperator*{\fiint}{\ensuremath{\iint\text{\kern-1.36em{\raisebox{5.87pt}{\rotatebox{-93}{$\setminus$}}}}}}.

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Borrowing (stealing?!) some code from the posting The Principal Value Integral symbol, here are suggested versions of \dashiint and ddashiint; the former has a single horizontal bar going through the double-integral symbol, and the latter has a double horizontal bar. The following screenshot shows the symbols in display style and text (aka inline-math) style.

enter image description here

\documentclass{article}
\usepackage{amsmath}  % for \iint macro
\usepackage{graphicx} % for \rotatebox and \raisebox macros
\def\Xint#1{\mathchoice
   {\XXint\displaystyle\textstyle{#1}}%
   {\XXint\textstyle\scriptstyle{#1}}%
   {\XXint\scriptstyle\scriptscriptstyle{#1}}%
   {\XXint\scriptscriptstyle\scriptscriptstyle{#1}}%
   \!\iint}
\def\XXint#1#2#3{{\setbox0=\hbox{$#1{#2#3}{\iint}$}
     \vcenter{\hbox{$#2#3$}}\kern-.51\wd0}}
     
\def\longminus{\raisebox{-2ex}{\rotatebox[origin=c]{20}{${-}\mkern-3.5mu{-}$}}}
\def\longequal{\raisebox{-2ex}{\rotatebox[origin=c]{20}{${=}\mkern-3.5mu{=}$}}}  
\def\dashiint{\Xint\longminus}
\def\ddashiint{\Xint\longequal}

\begin{document}
$\displaystyle\dashiint\ddashiint$
$\dashiint\ddashiint$
\end{document}

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