How to prove p ( x ) ≥ m 2 / 4Let F be a...
How to prove
Let be a family of m subsets of a finite set X. For , let p(x) be the number of pairs (A,B) of sets such that either or . Prove that .
In the book I'm studying, writer has written the following hint:
Hint: Let d(x) be the degree of x in , and observe that .
I was wondering if someone could help me about my problem. Thanks in advance.