[texhax] Constructing a very thin space

[Philip Taylor]

Paul Isambert wrote:
> Units can be followed by an optional space, so they’re not
> “self-terminating”;

Yes, they take an /optional/ space, which is not quite
the same as a <space> being /expected/.

 if \thinspace did not include a space in its
> definition, expansion would continue until a space is found, see:
>
>     \def\aspace{ }
>     a\kern0pt\aspace b
>
> with no space between the two letters. Similarly, “a\kern0ptb” and
> “a\kern0pt b” are the same thing. So the space at the end of
> \thinspace is quite important.

It may indeed be :  I think I am beginning to see why.  But you
last example seems to be more of a counter-example :  if
“a\kern0ptb” and > “a\kern0pt b” are the same thing, then
the space is /not/ important, I would suggest.

However, returning both to Karl's original thesis and your
own variant thereof, it would seem that if one wants to avoid
a following token (or tokens, if the first expands to empty)
being expanded solely by virtue of TeX searching for "one
optional space", then including that space in the definition
(or by including \relax in its place) can indeed be required.

** Phil.