[texhax] Some puzzling TeX

Uwe Lueck uwe.lueck at web.de
Thu Feb 17 13:20:53 CET 2011

Isn't this one of the (rather rare) cases where the documentation of latex.ltx 
-- source2e.pdf, ltdefns.dtx -- is quite comprehensive? 

    The following code makes \@sptoken a space token. It is important here that the
control sequence \: consists of a non-letter only, so that the following whitespace is
significant. Together with the fact that the equal sign in a \let may be followed
by only one optional space the desired effect is achieved.

(TeXbook p. 277, "<let assignment>".)

"RTFM"! - ) -- Uwe

"Rod Harries" <rod at harries.net.nz>, 17.02.2011 00:44:25:
> I am trying to understand why  one would write
> \def\:{\let\@sptoken= } \: %
> instead of just \let\@sptoken=   %
> or \def\@sptoken{ }

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