Published online by Cambridge University Press: 18 February 2004
The purpose of this note is to call attention to an error in the paper [1]. The main result was a new proof of the main theorem in [2]. In line 1 of page 446 of [1] one finds the following remark: “This is the result obtained in [2]”. However, a comparison of the two results shows that the generator which is called $d_1 d^{-1}_2$ in the notation of [1] appears in [2] but is missing from the list in [1].