The Romanian-born American artist Saul Steinberg is best known in this country for his cartoons and New Yorker covers, and for such books as The Passport and The Inspector. This week a retrospective exhibition covering 40 years of his paintings. collages, tables and graphic work opens at the Serpentine Gallery in London, enabling the British public to see for the first time the full range of his achievement. John Hollander, poet and Professor of English at Yale, has long been an admirer of Steinberg. He examines the development of his work and world.