A generation of symbols asserted for n ≥ 0 in the proof of Theorem 3.3 of the original paper in fact only holds for n > 0, thus
undermining the proof of the theorem. A new version of Section 3.5 of the original paper is given, culminating in a corrected proof
of Theorem 3.3. The author thanks Deepak Khosla for pointing out the gap in the previous version of the proof.