Joshua Foer might be the least-known of the Foer brothers, but after his first book, Moonwalking with Einstein, he might not hold that title for long. The nonfiction book, originally meant to depict competitors in the National Memory Championship from the outside, evolved into a chronicle of Foer’s own entrance into the memory world, combining the story of Foer’s training with anecdotes and studies on the topic of memory; tonight at Greenlight Bookstore, Foer will read from it. A.J. Jacobs, who documented his attempt at Old Testament-style life in The Year of Living Biblically, will introduce the younger Foer.