[NTG-context] definemathsymbol and txfonts

Hi, I can't figure out how to get \definemathsymbol work with txfonts extended-A math fonts: \definemathsymbol [oiint] [op] [txexa] ["09] \starttext I want to get this: \getglyph{txexa}{\char"09} \startformula \oiint f(x,y) \,da \stopformula \stoptext Thanks for any help, David