[NTG-context] Sum and mathalignment

Dear list, [image: image.png] What I've done is to play with mathalignment and \framed. Here is a MWE: \starttext \defineoverlay[midrule][{\blackrule[height=.02cm,width=5.5cm]}] \framed[frame=off,background=midrule,boffset=.65cm]{\startformula \startmathalignment[n=12,align={middle,middle,middle,middle,middle,middle,middle,middle,middle,middle,middle,middle}] \NC \NC S_6 \NC= \NC 1 \NC+ \NC 2 \NC+ \NC\dots \NC+ \NC 5 \NC+ \NC 6 \NR \NC + \NC S_6 \NC= \NC 6 \NC+ \NC 5 \NC+ \NC\dots \NC+ \NC 2\NC+ \NC 1 \NR \NC\NC 2S_6 \NC= \NC 7 \NC+ \NC 7 \NC+ \NC\dots \NC+ \NC 7 \NC+ \NC 7 \NR \stopmathalignment \stopformula} \stoptext Is there a simpler way to typeset something like this? Thanks in advance!