[NTG-context] how to do something like ^1/_2 with frac?

Hi all again, I try to do something like 1/2 with an upper 1 and a lower 2. The code below still doesn't quite work. \def\nfrac#1#2{\leavevmode\kern.1em% \raise.5ex\hbox{\scriptsize #1}% \kern-.1em/\kern-.15em% \lower.25ex\hbox{\scriptsize #2}} Help would be very much appreciated! Hubertus P.S. Is there a good pdf around to get some insight's of this tex-magic?