L165100 - Fall 2010 - Homework 1
1. Prove that the distance between any two vertices of a connected graph G (that is, the length of a shortest walk between these vertices) is less than the number of distinct eigenvalues of G.
2. Find the eigenvalues of the complete bipartite graph Km,n in two different ways: by linear algebra and by counting closed walks.
3. Find the number of closed walks of length` in the graph below.
r r r
r r r
r r r
4. Show that a finite poset can be covered by k antichains if and only if it does not contain a(k + 1)-element chain.
5. How many antichains of maximal size are there in the Boolean poset Bn?
1