Full of mischief and valor, ribaldry and romance, The Arabian Nights is a work that has enthralled readers for centuries. The text presented here is that of the 1932 Modern Library edition for which Bennett A. Cerf chose the "most famous and representative" of the stories from the multivolume translation of Richard F. Burton.    The origins of The Arabian Nights are obscure. About a thousand years ago a vast number of stories in Arabic from various countries began to be brought together; only much later was the collection called The Arabian Nights or the Thousand and One Nights. All the stories are told by Shahrazad (Scheherazade), who entertains her husband, King Shahryar, whose custom it was to execute his wives after a single night. Shahrazad begins a story each night but withholds the ending until the following night, thus postponing her execution.    This selection includes many of the stories that are universally known though seldom read in this authentic form: "Alaeddin; or, the Wonderful Lamp," "Sindbad the Seaman and Sindbad the Landsman," and "Ali Baba and the Forty Thieves." These, and the tales that accompany them, make delightful reading, demonstrating, as the Modern Library noted in 1932, that Shahrazad's spell remains unbroken.