[texhax] Error in argument of \section.

[Robin Fairbairns]

>       There may be an error in the \section command of Latex2e. I get an 
> "Illegal parameter in the definition of..."  error message when I include the 
> \overrightarrow command in the math mode in the argument of the \section command. 
> Enclosing a stripped down version of an example. Could you please comment?

a simple consideration of probabilities would have led you to realise
that such an error was improbable.

as documented, when \section has no optional argument, the argument is
a moving one.  \overrightarrow is a fragile command.  fragile commands
regularly produce odd error messages in moving arguments.

convert your file to

  \documentclass[12pt,noamsfonts]{amsbook}
  \begin{document}
  \section{$\protect\overrightarrow{A}$}
  \end{document}

and it works.