Who can resist tampering with history? Parts of the book appeared originally as a serial and a separate novelette. The redundancies this created have been removed, as have some non-value-added sections of less than immortal prose and the odd adverb or two. Futuristic references to "the national DataNet" have been amended to "the Internet." There are a few other changes of that sort from the first edition. Others, like the new-demolished viaduct in downtown Denver, have been left in place. There are limits to revisionist history.

The essay "An Introduction to Cliology" (originally "An Introduction to Psychohistory") was added at the request of readers at various SF conventions.

My thanks to Stan Schmidt of Analog magazine for publishing the earlier serial, novelette, and article; and to Jim Baen, who published the first edition, now long out of print. Thanks also to my agent, Eleanor Wood, who called one day and asked, :Have you ever thought about writing a novel?"

Michael Flynn Easton, Pennsylvania 2001