I got 3 suggestion.
let the backspace key repeat if user tap then hold it.... it's very annoying try deleting multiple characters.
a stronger backspace key. Currently, as far as I know,1+cos(x)*sin(x)When one try delete "sin(x)", he will have to press backspace 6 times.... I believe you guy can think up a better way then that, right?
User defined keyborad. Let users define a keyboard layout ( or even plural?) to speed up some input one find he use a lot.... say "%lineNo"
Thanks for the feedback. These are great suggestions.