% This is overrightarrow.sty, It provides for a command:
% \Overrightarrow which is somewhat like \overrightarrow and somewhat
% like \Rightarrow.  Also a couple of helper commands.
% This file is public domain.
% James Kilfiger mapdn@csv.warwick.ac.uk
%
\newcommand\reldoublebar{\mathrel{\smash=}}
\newcommand{\Rightarrowfill@}[1]{%
\m@th \setboxz@h {$#1\reldoublebar $}\ht \z@ \z@ 
$#1\copy \z@ 
\mkern -6mu\cleaders \hbox {$#1\mkern -2mu\box \z@ \mkern -2mu$}\hfill 
\mkern -6mu
\mathord \Rightarrow $}
\newcommand{\Overrightarrow}{\mathpalette{\overarrow@\Rightarrowfill@}}