I use
\mathrm{K}^{+}
to get an upright K^+ (K-Ion) (and other items such as units)
and guess the following message on the terminal from which I start lyx has
to do with it: [Unknown [sub [mathrm [char E mathalpha]] [char e mathalpha][char x mathalpha]]] Do I have to include some package or use another method? Wolfgang
