put a rightharpoonup over AB ?

[jojo...@ms25.hinet.net]

Is it possible to put a rightharpoonup over AB.
like the one below:
__\
AB
(or see the symbol in the Exam Paper
http://www.ceec.edu.tw/AbilityExam/AbilityExamPaper/94AbExamPaper/94math.pdf)
Someone tell me
$\overset{-\!\!-\!\rightharpoonup}{AB}$ will work,
but I think the distance between the harpoon and AB
is too great (compare with $\overline{AB}$).

Any ideal?
Thanks
Joe

[Lars Madsen]

something like this:

\documentclass{article}
\usepackage{amsmath,amssymb}
\makeatletter
\def\rightharpoonupfill@{\arrowfill@\relbar\relbar\rightharpoonup}
\newcommand{\overrightharpoonup}{%
\mathpalette{\overarrow@\rightharpoonupfill@}}
\makeatother
\begin{document}
$\overrightharpoonup{AB}$
\end{document}

(surely some package have already defined this?, made by looking at the
definiotn of \overrightarrow in amsmath.sty)

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