[texhax] Double bar?

[Philipp Stephani]

Am 01.01.2011 um 20:15 schrieb Rodolfo Medina:

> Hi to all TeX users.
> 
> I wish to put a double bar onto a math symbol, in particular over `x', but
> `$\bar \bar x$' gives error and `$\bar{\bar x}$' is not very nice because the
> two bars are not precisely aligned.  Please help on this issue (I'm a plain TeX
> user).

The plain format has the \skew macro for exact (manual) placement of double accents. See e.g. section 21.4 of TeX by Topic for an example.