In his beautiful booklnvisible eities Italo Calvino writes about the two cities ofValdrada, the one which lies on the shores of a lake, and the other which is reflected in the lake and contains not only the exterior of Valdrada on the shores, but also its interior, and probably its inhabitants. "Valdrada's inhabitants know", writes Calvino, "that each of their actions is, at once, that action and its mirror image . . . and this awareness prevents...