UK TeX FAQ -- question 210

### The Principal Value Integral symbol

This symbol (an integral sign, 'crossed') does not appear in any of the fonts ordinarily available to (La)TeX users, but it can be created by use of the following macros:

    \def\Xint#1{\mathchoice
       {\XXint\displaystyle\textstyle{#1}}%
       {\XXint\textstyle\scriptstyle{#1}}%
       {\XXint\scriptstyle\scriptscriptstyle{#1}}%
       {\XXint\scriptscriptstyle\scriptscriptstyle{#1}}%
       \!\int}
    \def\XXint#1#2#3{{\setbox0=\hbox{$#1{#2#3}{\int}$}
         \vcenter{\hbox{$#2#3$}}\kern-.5\wd0}}
    \def\ddashint{\Xint=}
    \def\dashint{\Xint-}

`\dashint` gives a single-dashed integral sign, `\ddashint` a double-dashed one.