Before revision:  Given a stream of n items from a data universe U ( equipped with a total order ) , the task is to compute a sketch (data structure) of size poly(\log(n), 1/\varepsilon).
After revision:  Given a stream of n items from a data universe U equipped with a total order ) , the task is to compute a sketch (data structure) of size poly(\log(n), 1/\varepsilon).