Eight original variations on well worn future,probing themes -- ""The Generation Gap,"" rites of passage, competition generated by psychological engineering, interterrestrial brotherhood, and a return to the land by the sons of a dead-end technology. Even Barry Malzberg's ""Over the Line,"" described by Elwood as ""new wavish,"" is far from experimental in any sense, but the contributors -- including Raymond F. Jones, Chad Oliver, and Thomas N. Scortia -- manage their tasks with professional dispatch. And here and there, as in Terry Carr's ""Rejoice, Rejoice, We Have No Choice,"" they manage a hint of emotional complexity. Lightweight.