What's the best practice to typeset Knuth's up-Arrow notation?
\upuparrow are relation symbols (according to
unimath-symbols.pdf). But in Knuth's up arrow notation, these should be a binary operator. So, how should on treat this difference?
Secondly, should double up arrows be typeset as
\upuparrow or as
\uparrow\uparrow, which illustrates the double nature better.