Update chapter_4.md
## Example Applications
-In this chapter we use the tools we have begun to develop, writing computations and changing their inputs, to affect somewhat more interesting computational patterns. Our goal is to build up to an interactive graph computation that supports both interactive queries and real-time updates to the graph structure.
+In this chapter we use the tools we have begun to develop, writing computations and changing their inputs, to effect somewhat more interesting computational patterns. Our goal is to build up to an interactive graph computation that supports both interactive queries and real-time updates to the graph structure.
These aren't the limits of differential dataflow, and we expect that you can also come up with new idioms for using the tools differential dataflow provides!
