This app generates .pdf documents of addition and/or subtraction 
exercises with numbers in the range specified by the user.

Currently, there are some rough edges, like no validation, poor 
typesetting, etc. Also, multiplication/division are not yet supported.

But it works. I'll add features, and clean things up over time, and
if there is anything you would particularly like, just let me know,
and I'll work on it sooner.