David Anick and Jan-Erik Roos have pointed out that Lemma 2 (the 'trick of Svarc') of [McC-ZI does not hold in the generality stated. The simplest counterexample is the manifold Sln. The key role played by this lemma in the proof of the main theorem of the paper requires that an alternative to the lemma be given and a re-examination of the details of the proof of the main theorem be undertaken. The methods of [McC] and [Sh] provide just such a substitute for the lemma as follows.