1 Both terms are open to attack by a purist, for different reasons; but the interpretation is correctly understood.
2 Gradients of other vector quantities, appearing later in this chapter, follow the same protocol.
4 Mostly, we expect μi(a) > 0. But, in degenerate cases, μi(a) = 0 along with gi(a) (x*) is also possible. How do you interpret such a case?
7 also called the method of multipliers