\starttext
\def\test#1#2%
{\begingroup
#1\relax
#2\relax
\writestatus{t1}{\the\mathatomglue\mathbinarycode\mathordinarycode\textstyle }
\writestatus{s1}{\the\mathatomglue\mathordinarycode\mathbinarycode\scriptstyle}
\writestatus{t2}{\space\space\the\binordspacing\textstyle }
\writestatus{s2}{\space\space\the\ordbinspacing\scriptstyle}
$k-1 <> 2^{k-1}$
\vskip-.9\lineheight
\endgroup}
\test{}{}
\test{\binordspacing\scriptstyle\binordspacing\textstyle}
{\ordbinspacing\scriptstyle\ordbinspacing\textstyle}