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

[Wenlin Institute]

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.
<to be read again>
                    \crcr
\oalign ...z at skip \lineskip .25ex\ialign {##\crcr
                                                   #1\crcr }}
\d ...1\crcr \hidewidth \sh at ft {-1ex}.\hidewidth }
                                                   }
l.1 \edef\test{\d{u}
                     }
------------------------------------------------------------

This happens with either pdftex or just tex (running at the command  
line on OS X 10.4.9):

This is pdfeTeX, Version 3.141592-1.30.4-2.2 (Web2C 7.5.5)
This is TeX, Version 3.141592 (Web2C 7.5.5)

The definition of \d is on page 356 of The TeXbook.

Any explanation, solution, or workaround will be greatly appreciated!

Best wishes,

Tom Bishop

文林 Wenlin Institute, Inc.        Software for Learning Chinese
E-mail: wenlin at wenlin.com     Web: http://www.wenlin.com
Telephone: 1-877-4-WENLIN (1-877-493-6546)
☯