csc 104 week 5

As the final exam coming soon, I start becoming little busy in computer science than before, however, during this week, I still working on the recursion to preparing for the quiz tomorrow, and start to realize what is flatten doing the DR.Racket. Also I did some review for how to writing check-expect for some program. However, I forget how to a tiny bit about the triangle recursion:( Flatten is one of the biggest problem I've been met since I join in the class.