# Zwiebach page 225

1. Oct 28, 2007

### ehrenfest

1. The problem statement, all variables and given/known data
Shouldn't there be an

$$\alpha_{-1}\alpha_{1}$$

added to equation 12.130 on account of equation 12.129, or is that 0 for some reason?

2. Relevant equations

3. The attempt at a solution

2. Oct 28, 2007

### Jimmy Snyder

If you work out the sum of the commutators of the terms in parentheses in equations (12.125) and (12.126), and use equation (12.128), you will find it deficient from $4L_0$ by exactly $\alpha_{-1}\alpha_1$.