Now, Pattern.begin("a").notFollowedBy("b") is not allowed in CEP. But this a useful in many applications. Such as operators may want to find the users who created an order but didn't pay in 10 minutes.
So I propose to support that notFollowedBy() with a interval can be the last part of a Pattern.
For example, Pattern.begin("a").notFollowedBy("b").within(Time.minutes(10)) will be valid in the future.