[texhax] [TeXhax] Latex: dumbing down ?

[Reinhard Kotucha]

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

  > Reinhard Kotucha wrote:

  >> The definition of \@ifundefined is
  >> 
  >> \expandafter \ifx \csname #1\endcsname \relax \expandafter
  >> \@firstoftwo \else \expandafter \@secondoftwo \fi
  >> 
  >> Hence, if someone says \@ifundefined{foo}{}{} and tries later
  >> \ifx\foo\undefined this will always succeed because \@ifundefined
  >> sets undefined cotrol sequences to \relax.

  >> You cannot safely use \ifx in LaTeX.

  > No no.  It is \csname ... \endcsname that "sets undefined control
  > sequences to \relax", as every Plain TeX hacker knows

If \@ifundefined is defined as it is, it sets undefined control
sequences to \relax.  Full stop.  Of course it is actually done by
\csname ... \endcsname.  Not only plain tex hackers (whatever this
means) know this.

Cheers,
  Reinhard

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