I would like to ask two questions about Hund's rules and L-S coupling: 1. Some textbooks state that when doing L-S coupling and applying Hund's rules, "The maximum values of S and L are subject to the condition that no two electrons may have the same pair of values for m(sub s) and m(sub l). I know this is because of the Pauli exclusion principle, but how does this requirement (m(sub s) and m(sub l)) really limit S and L when we are adding the angular momenta? 2. When we are trying to figure out the ground state of Sm (4f)6, why is it wrong to have L = Sum(l) = 6*3? Finally, I've realized that in discussing Hund's rules and L-S coupling some texts tend to make explanations using symmetry consideration and the others tend to prefer the exclusion principle. Are they two different sets of explanations, or are they equivalent?