I just posted and found something weird. The 'limit' tag worked in preview, but then in post it changed the "h -> 0" to a subscript - not an underscript, namely:
The 'norm' tag does not work, so I used double vertical bars .
[I] the limit: (from The Art Of Problem Solving)
"That summation symbol is a little ugly. We can make it prettier by using the \displaystyle:" (edited for this thread)
[II] the norm:
backslash norm
piped normvs
[III] Here are more symbols than one should be allowed to know:
The Comprehensive LaTeX Symbol List.aka