[texhax] Oblique cancellation with plain TeX

[James Diamond]

On Fri, Jan  4, 2019 at 19:14 (+0000), Rodolfo Medina wrote:

> Philip Taylor <P.Taylor at Rhul.Ac.Uk> writes:

>> Maybe if you were to post a GIF/PNG/JPG/PDF of the effect you are trying to
>> create, we non-mathematicians might be better placed to help you ...


> The following is a simple example: to be processed with simply `latex file'.  I
> want the same but with plain TeX...  Thanks,

> Rodolfo

> \documentclass[preview,border=12pt,varwidth]{standalone}
> \usepackage{cancel}
> \begin{document}
> \abovedisplayskip=0pt
> \[
> \frac{a\cancel{b}}{\cancel{b}}=a
> \]
> \end{document}

What is wrong with

$$ {a\rlap{$b$}/ \over \rlap{$b$}/} = a$$

(Aside from the fact that if $b = 0$ then Bad Things are happening?)

You could also write

\def\cancel#1{\rlap{$#1$}/}

somewhere near the beginning of your document and then, when you want
to cancel things out, write something like

$$ {a\cancel{b} \over \cancel{b}} = a$$

or

This is $ {a\cancel{b} \over \cancel{b}} = a$ a simple idea.





Cheers.

                                Jim