Alternate-world yarns exert an endless fascination: for one, because other worlds are scientifically respectable (modern particle theory admits the possibility); for another, the godlike power offered by historical what-ifs (for instance, what-if the Nazis had won WW II? Or what-if Christ had never been born? Examples of both are to be found here). Anyhow, these 14 tales, 1968-92, include several famous entries. Fritz Leiber's waggish ``Catch That Zeppelin!'' features Hitler as an airship salesman. In Kim Stanley Robinson's ``The Lucky Strike,'' the atom-bombing of Japan doesn't go exactly as planned. And Eisenhower plays clarinet with Louis Armstrong while Senator E.A. Presley applauds, in Howard Waldrop's amusing ``Ike at the Mike.''