6.4 Symmetric dierence kernel. Let X be a nite set. Show that the kernel K dened over 2X, the set of subsets of X, by 8A;B 2 2X;K(A;B) = exp



????

1 2jA
Bj



;

where A
B is the symmetric dierence of A and B is PDS (Hint: you could use the fact that K is the result of the normalization of a kernel function K0).