# [texhax] Can't use \d (dot below) with \edef

Philip & Le Khanh Philip-and-LeKhanh at Royal-Tunbridge-Wells.Org
Tue Jun 19 13:01:39 CEST 2007

```Nasty.  This shews the cause --

\edef \test {\halign {#1\crcr \crcr}}

but I can't remember whether this is documented.

Philip Taylor
--------
Wenlin Institute wrote:
> Dear TeX typesetters,
>
> There is a problem with the Plain TeX macro \d for adding a dot below
> a letter. Generally it works fine, but in a certain context it causes
> an error, as illustrated by the following very short TeX program:
>
> \edef\test{\d{u}}\bye
>
> The error message is:
>
> ------------------------------------------------------------
> ! Illegal parameter number in definition of \test.