P.43: In the display, the equation defining P2 should be: P2 = Im(1-e) = Ker(e).
P.50: The last line ("nonzero powers ...") should instead be the last line on p.51.
P.52: In the third line of the proof of Theorem 6.4, the statement that direct limits respect the property of being semihereditary is incorrect; see [35, Example 4.2]. However [35, Theorem 3.4] leads to a stronger result than that of the abovementioned theorem; namely, that Theorem 6.2 holds without the finite generation condition.
Pp.68-75, sections 10-11: most of the questions raised in these sections are answered in .
Notes on the other papers listed below:  is closely related to , though the latter does not depend on it.  gives an example stronger than that of Example 10.2 of this paper, which also answers the question in the paragraph before that example.  inter alia corrects an error in .
 George M. Bergman and Warren Dicks, On universal derivations, J. Alg. 36 (1975) 193-211. MR52#8196.
 George M. Bergman and Warren Dicks, Universal derivations and universal ring constructions, Pacific J. Math. 79 (1978) 293-337. MR81b:16024.
 Robert A. Indik, A PI-algebra which is not PI when an inverse is adjoined, Proc. A. M. S. 76 (1979) 11-13. MR80d:16015.
 P. M. Cohn and Warren Dicks, Localization in semifirs, II, J. London Math. Soc. (2) 13 (1976) 411-418. MR54#12814.
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