Week 5 ,Lecture#1, #2

I believe week five lectures were about recursion concept .
The slide # 8, 9 from week #5 , lecture#2, I could not get them at all. If I am right, It should be chapter four materials related to set.

The closed-form concept is cumbersome job. I think first, I have to do unwinding on general given function after analyzing the output of function I have to derive closed-form formula from the output of general function. Then I have to prove it that the closed-form formula works.

I hope, I am right here.