Middle of page 363 - first paragraph below the box:
“In the example here, we sell the precise number of futures to completely hedge the stock portfolio. The stock portfolio, however, has to be identical to the index. It cannot have a different beta. The other formula, which reduces the beta to zero, is more general and can be used to eliminate the systemic risk of any portfolio.”
I rarely understand these things through and through, so I must be wrong somewhere. I just don’t know where.