Oblique cancellation with plain TeX

[Rodolfo Medina]

Rodolfo Medina <rodolfo.medina at gmail.com> writes:

> David Carlisle <d.p.carlisle at gmail.com> writes:
>
>> \input picture
>> \catcode`\@=11
>>
>> \RequirePackage{cancel}
>> \let\zzcancel\cancel
>> \def\cancel#1{{%
>> \let\line\LaTeX at line
>> \zzcancel{#1}}}
>>
>> $\cancel{x^2 + 1}$
>>
>> $\cancel{a}$
>>
>> $\cancel{{x^2 + 1 \over b}}$
>>
>>
>> \bye
>
>
> Fantastic...!!


Strange...  Now I'm on a different computer of mine and I get error:

$ tex test
This is TeX, Version 3.14159265 (TeX Live 2016/Debian) (preloaded format=tex)
(./test.tex (/usr/share/texlive/texmf-dist/tex/plain/graphics-pln/picture.tex
(/usr/share/texlive/texmf-dist/tex/plain/graphics-pln/miniltx.tex)
(/usr/share/texlive/texmf-dist/tex/plain/graphics-pln/autopict.sty))
(/usr/share/texlive/texmf-dist/tex/latex/cancel/cancel.sty)
! Undefined control sequence.
\@cancel ...eight \unitlength \p@ \canc at thinlines 
                                                  {\/\raise \dimen@ \hbox {\...

\mathpalette ...>\mathchoice {#1\displaystyle {#2}
                                                  }{#1\textstyle {#2}}{#1\sc...

\zzcancel ...lette {\@cancel {\@can at slash {}}}{#1}
                                                  \else \@cancel {\@can at slas...

\cancel #1->{\let \line \LaTeX at line \zzcancel {#1}
                                                  }
l.10 $\cancel{x^2 + 1}
                      $
? 


Maybe a too old version of `picture'...?  In fact, on this PC, I have an older
version of Debian...

Thanks for any help,

Cheers,

Rodolfo