[NTG-context] font error?

Just experimenting somewhat with fonts. Could the following be a font problem? Or is it just not possible in this typeface (taken from "fonts in context" page 70) Example: \def\thetypeface{asana} \setupbodyfont[\thetypeface] \starttext [\thetypeface]\quad Hello world!\space$c = \sqrt{a^2+b^2}$ \stoptext Log message: ! Math error: parameter \Umathquad\displaystyle is not set. system > tex > error on line 4 in file test.tex: Math error: parameter \Umathquad\displaystyle is not set ... 1 \def\thetypeface{asana} 2 \setupbodyfont[\thetypeface] 3 \starttext 4 >> [\thetypeface]\quad Hello world!\space$c = \sqrt{a^2+b^2}$ 5 \stoptext l.4 ...quad Hello world!\space$c = \sqrt{a^2+b^2}$ Hans van der Meer