Respected Professor,
I was going through the exercises, and in HW 9, exercise 3.1, I am unable to get the negative sign in the expression of \mathca{B}^2. Although the following inequalities remain unaltered, I am confused if I am doing something wrong. Could you please confirm once? This link also suggests that it should be a + before the commutators.
Thank you.
Yours sincerely,
Khurshed Fitter
