On 26/08/2011, at 3:04 AM, Ulrike Fischer wrote:

> Now I want to define a "mirrored" key  
> 
> no-sym 
> 
> so that "no-sym = true" sets  \l_chessfss_sym_bool to false. 
> 
> Is there some easy way? 

Not directly as far as I know (using

  .code:n = { \bool_set_false:N \l_chessfss_sym_bool }

works of course but it's not the best interface), so I think this would be a good addition. (I seem to remember kvoptions has a similar feature.) Which do you think is best to name it?

  no-sym .bool_unset:N = \l_chessfss_sym_bool 
  no-sym .bool_set_false:N = \l_chessfss_sym_bool 
  no-sym .bool_set_reverse:N = \l_chessfss_sym_bool 

Cheers,
-- Will