[NTG-context] MetaPost graphics within formulas

Hi there, maths can sometimes be weird and even more so the kinds of formulas one needs to typeset occasionally ;-) So here I need to typeset triangles and a variety of other polygons right in the middle of a display formula. What I've been able to come up with so far is something like this: --- \starttext \startuseMPgraphic{tetrahedral} u := 10pt; draw (0,0)--(2u,0)--(u,sqrt(3)*u)--cycle; \stopuseMPgraphic \startformula \Phi(\useMPgraphic{tetrahedral})=F_{kln}^{ijm}\,v_iv_jv_kv_l\, \delta_{j^*nk^*}\,\delta_{l^*n^*i^*}\,\Phi(\emptyset) \stopformula \stoptext --- Now if I only knew how to properly align my MetaPost figure with the rest of the formula … any ideas? Cheerio, Oliver