I thank A. Dubois for bibliographic information and D. Marjanović for comments on the draft. N.J. Kluge and two anonymous reviewers provided detailed comments that helped improve the paper, even though I could not follow some of them because of disagreements on basic issues.
Received: 1 June 2010
Revised and accepted: 31 August 2010
Published online: 20 October 2010
Editor: J.W. Arntzen