THE UNICORN (311 pp.)Iris MurdochViking ($5).
In a gesture that seems both apologetic and pompous, Graham Greene has insisted that his light novels (those in which God does not have a speaking part) should be called "entertainments." The tag does not fit all light novels, because it carries the implication that the author can write much more deeply when he cares to. But it suits exactly the books of Iris Murdoch, a professional philosopher and former Oxford don. whose only equal as an entertainment writer is Greene himself.
Murdoch entertainments are usually very witty and more than a little strange. Enthusiasts cherish such...