Or just unicode. Standard digraphs ftw (xcompose, wincompose...). It's even typed in the same way (_4 ^+ etc) - and maybe there's tex tools that output unicode these days where possible?
true, true... I wonder if that's even possible to do in unicode. maybe some combining char thing. I certainly wouldn't be able to type a digraph of it from memory if it is. But, I feel it's still more readable this way
H₂O, NH₄⁺, NO, HCO₃⁻, HPO₄²⁻