# [texhax] Obsolete \centerline command used in amsbook class (Uwe L?ck)

Philip TAYLOR P.Taylor at rhul.ac.uk
Thu Sep 27 14:57:33 CEST 2012


Ulrike Fischer wrote:

> Exactly. I don't care when people make a lot of fuss about a very
> small nuisance. The amslatex team certainly did not change \over out
> of a whim. The reasons are explain in the technotes:
> ftp://ftp.ams.org/ams/amslatex/math/technote.pdf

With the greatest respect, the reasons are /not/ explained : rather,
Michael shews how the presence of \over massively complicates TeX's
mathematical internals [1] (something that no knowledgeable TeX user
would deny).  But removing the user-level interface to \over makes
not one iota of difference; TeX /still/ has to jump through the hoop
in order to typeset mathematics, and no amount of tampering with the
user interface (and concealing useful TeX primitives) can change that.

Thus I would argue that the AMSLaTeX team were tackling the symptoms,
not the disease, and that their tampering (in this case) was both
unjustified and counter-productive.

Philip Taylor
--------

[1]

> Not only is the unusual syntax of the TEX primitives rather out of
> place in LATEX, but furthermore that syntax seems to be responsible
> for one of the most signi
cant aws in TEX's mathematical typesetting
> capabilities: the fact that the current mathstyle at any given point
> in a math formula cannot be determined until the end of the formula,
> because of the possibility that a following generalized fraction
> command will change the mathstyle of the preceding material. To cite
> two of the worst side e
ects: \mathchoice must actually typeset all
> four of its arguments, instead of being able to immediately select
> only one; and, were it possible to always know the current math
> style at a given point, math font selection would be greatly
> simpli
ed and the upper limit of 16 di
erent math font \fams would
> never be a problem as \text,script[script]font assignments for any
> \fam could take immediate e
ect and therefore could be changed
> arbitrarily often within a single formula. More concretely, math font
> selection diculties are responsible for many of the more convoluted
> passages in the source code of LATEX's NFSS (that does font loading
> on demand) and of the amsmath package, and by extension it has
> historically been responsible for signi
cant delays in making new
> features available to end users and for making those features more
> the syntax of those generalized fraction commands that only become
> evident when you do some writing of nontrivial macros for math use.
> For example, as things currently stand you cannot measure the size of
> any object in math without going through \mathchoice and leaving and
> reentering math mode via \hbox{\$ (which then introduces complications
> regarding \everymath and \mathsurround). And it seems that
> uncertainty about the current mathstyle is the only barrier to
> allowing the use of mu units with \vrule, to make vertical struts in
> constructing compound symbols or notation. And so on and so forth.