[OS X TeX] how to produce a wide arc?

[Luis Sequeira]

It is easy to produce extensible "accents" in math, such as \widehat 
{ABC} or \widehat{ABCDEFGHIJ} (where the "hat" extends as needed to  
encompass the width of the argument). Similarly for \overbrace{}, and  
so on.

I would like to do something like for representing arcs: something  
like \arc{AB} should put an arc above the letters.
I can sort of simulate it by putting \frown above the letters, i.e.
  \newcommand{\arc}[1]{\overset{\frown}{#1}}

but this of course does not stretch.

I can "almost" do it with the code below, but for reasons that I  
can't fathom the arc does stretch but appears misaligned with the  
text (it is shifted to the right somewhat).

Now maybe:

1) there already is some command to do it; or
2) someone can find the fault in the code below...

\newlength{\arclen}
\newlength{\archeight}
\settoheight{\archeight}{$\frown$}

\newcommand{\arc}[1]%
{\settowidth{\arclen}{#1}%
\overset{\resizebox{\arclen}{\archeight}{$\frown$}}{#1}}


If replying to the list, I'd appreciate cc: to my address (as I'm on  
digest).

TIA

Luis Sequeira

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