[texhax] Oblique cancellation with plain TeX

[Rodolfo Medina]

James Diamond <jim.diamond at acadiau.ca> writes:

> 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.


Well, thanks, Jim, but...  sorry, it's my fault...  I'd better better explain
myself...  It's needed that the argument of \cancel may be variable, and so the
diagonal line should also vary its length and angle:

\documentclass[preview,border=12pt,varwidth]{standalone}
\usepackage{cancel}
\begin{document}

$\cancel{x^2 + 1}$

$\cancel{a}$

$\cancel{{x^2 + 1 \over b}}$

\end{document}


Rodolfo