first = 'Joe went to the store and bought 2 loaves of bread'
second = 'Joe and I went to the market and bought 3 loaves of bread
and butter'

assert_equal [4..9, 21..29, 57..68], diff(first, second)  # diff()
returns a list of Ranges spanning the position of edits or insertions

Anyone know an algorithm (or code) that can make that work?