e
Command/ mathextensible
Command/ mathframed
Command/ mathmatrix
Command/ mathornament
Command/ mathoverextensible
Command/ mathovertextextensible
Command/ mathradical
Command/ mathtriplet
Command/ mathunderextensible
Command/ mathundertextextensible
Command/ mathunstacked
Command/ nextparagra
but I
woul dlike to have an elegant solution in ConTeXt.
%%% begin interior-of-a-set.tex
\showgrid
\starttext
\mathtriplet{A}{\circ}{}
\startformula
\mathtriplet{A}{\circ}{}
\stopformula
\stoptext
%%% end interior-of-a-set.tex
Thanks for your help: OK