Uwe Lueck uwe.lueck at web.de
Sat Oct 30 13:06:51 CEST 2010

"Michael Barr" , 29.10.2010 18:01:49:
> \def\bbrack#1{[\![#1]\!]}
> $\bbrack{\widehat c =\widehat d}$
>
> Yes, I could add extra space after the argument, but that is a real
> kludge.  My real question is why can't I get the \widehat to actually be
> centered over its argument.  As you can see, it starts halfway along the
> "d" and ends well to the right.  This is also true of the one on the "c"
> so it is not just centering over an ascender.

Ok, I keep recommending my earlier $[\,CONTENT\,]$ for certain
CONTENTs, but I see it is a halfway solution if any.

"Donald Arseneau" <asnd at triumf.ca>, 30.10.2010 01:54:50:
> 1) the letter "d" has its high point over on the right, but the
> accent is centered over the entire letter, extrapolated along the
> slope.  If you take the wide part of the d, follow a sloped line
> up parallel to the stem, you nearly meet the apex of the hat.
> I bet you expect the hat to be aligned with the stem only.

So simply do so:

\newcommand*\Widehat[1]{\widehat{\hbox{$#1$}}}
\def\bbrack#1{[\![#1]\!]}
$\bbrack{\Widehat c =\Widehat d}$

or as recommended earlier:

$\bbrack{\,\Widehat c =\Widehat d\,}$

and if the argument of \bbrack will always have spaces from
relation symbols and the like, I would indeed recommend

\newcommand*\Widehat[1]{\widehat{\hbox{$#1$}}}
\def\bbrack#1{[\![\,#1\,]\!]}
$\bbrack{\Widehat c =\Widehat d}$

-- tested!

HTH -- Uwe.