7 Acknowledgement
I wish to thank Jürg Beer, John Brooke, Mausumi Dikpati, Antonio Ferriz-Mas, David Hathaway,
Mathieu Ossendrijver, and Steve Tobias for providing data and/or graphical material for inclusion in this
review; also Peter Gilman, Arnab Choudhuri, and Matthias Rempel for providing preprints
in advance of publication. The review also benefited from the constructive criticism of Peter
Gilman and Michael Stix. At this point, usually all that would normally be left for me to do is
to assure readers and colleagues that any error, omission or misrepresentation of their work
is not intentional, and to offer general advanced apologies to all slighted. Here however, the
organic format of Living Reviews allows actual amendments and additions. Please send your
comments/suggestions/criticisms to the above e-mail address. And for this I offer advanced thanks to all
future correspondents.
