# [texhax] the \let command

Uwe Lück uwe.lueck at web.de
Mon Nov 27 03:38:07 CET 2006

> > > On Fri, 24 Nov 2006, R.Tange at soton.ac.uk wrote:
> > >
> > > > Why does
> > > >
> > > > \let\mycedilla\c
> > > > \renewcommand{\c}{\ensuremath{\mathcal{c}}}
> > > >
> > > > work fine, but
> > > >
> > > > \let\tie\t
> > > > \renewcommand{\t}{\ensuremath{\mathfrac{t}}}
> > > >
> > > > go wrong?

At 01:08 27.11.06, Hartmut Henkel wrote:
> > > no, \tie points to the _former_ \t definition, then \t is redefined.
> > > They don't necessarily mean the same thing.
> >
> > ... I wonder, wonder -- somewhat boldly: will Rudolf Tange understand
> > this while I don't? "necessarily mean"? In fact, \meaning\t and
> > \meaning\tie agree (necessarily).
>
>in german it would be "nicht notwendigerweise" or "nicht zwingend",
>maybe my translation is bad. Well, from Rudolf Tanges original mail i
>had condensed a minimal example to see what's going on, and here is a
>version with what i have learnt in the meanwhile from you (eufrak) and
>
>\documentclass{article}
>\usepackage{eufrak}
>\begin{document}
>
>\let\tie\t
>\renewcommand{\t}{\ensuremath{\mathfrac{t}}}
>
>In fact, \meaning\t and \meaning\tie agree (necessarily).
>
>\end{document}
>
>(We should always use minimal examples.) Obviously \meaning\t and
>\meaning\tie in fact don't agree in this example (i described also,
>why). So it's not necessarily so, as it depends also on the past. E. g.
>one can force it, as you do by the double \renewcommand. But this was
>not part of the original question. If you want \meaning\t and
>\meaning\tie agree (necessarily), you can simply write:
>
>\renewcommand{\t}{\ensuremath{\mathfrac{t}}}
>\let\tie\t

... aha, sorry, a typical strange error of mine:

At 11:18 24.11.06, R.Tange at soton.ac.uk wrote:

>Why does
>
>\let\mycedilla\c
>\renewcommand{\c}{\ensuremath{\mathcal{c}}}
>
>work fine, but
>
>\let\tie\t
>\renewcommand{\t}{\ensuremath{\mathfrac{t}}}
>
>go wrong?
>
>After executing the above two lines \t and \tie mean the same thing.

It seems that, on its way from my eyes to my -- from an
evolutionary point of view -- most recent regions of my brain,
"two lines" turned into "two times" or so. My example appeared
to be not really minimal due to additional lines for "two times".

Now, the vagueness appears to be Rudolf's.
What is going wrong? What does "mean the same thing" mean?

E.g.: the \c thing may work because \mathcal has been defined,
while the \t thing doesn't -- because \mathfrac is undefined
(typo instead of \mathfrak, as Victor has pointed out).

So long,

Uwe.