I'm really struggling on even getting started on this problem. I have read the chapter several times now and I have tried to understand the explanations in the chapter. But I can't even get this problem started. All I ask is if anyone knows how to do this, can you just get me started or point me in the right direction so I can then take it from there? Thanks for any help. ___________ Prove the theorem <K|H|L> = (N!)1/2 <KHP|H|L> where |KHP> is the Hartree product corresponding to the determinant |K>, i.e. |K> = |Xm(X1)Xn(X2)...> and |KHP> = Xm(X1)Xn(X2)... Prove this theorem _______________ H = O1 + O2 O1 = h(1) + h(2) + ... + h(N) O2 = r12-1 + r13-1 + r14-1 + ... + r23-1 + r24-1 + ... + rN-1-1, N This problem is from "Modern Quantum Chemistry" by Szabo & Ostlund for anyone who is wondering.