how to draw this in RemNote?
\xymatrix{
A &*+[F]{\sum_{i=n}^m {i^2}} \
& {\bullet} & D \ar[ul] }
Render it somewhere else and paste it in as an image. RemNote uses KaTeX, which doesn’t support xy-pic. It does support array, so you could do it like that too, but it’s kind of a kludge.