Now available for the first time in paperback, John Fuller's ''A Commentary'' is a compendious yet condensed reference work dealing with all of Auden's writings. For every poem, play or libretto, Fuller encapsulates the publishing history, paraphrases difficult passages, explains allusions, points out interesting variants (including material abandoned in drafts), identifies sources and influences, looks at the verse form and offers critical interpretation. Auden's formal and intellectual range challenges comparison with Eliot or Yeats, and his particular interests - psychological, anthropological, prosodic, theological, historical - lend an added resonance to the texture of his work, all of which is explored and interpreted, with exemplary lucidity, in this most essential of one-volume companions.