In the original 1964 edition of The Ambidextrous Universe, Gardner quoted two lines of poetry from Vladimir Nabokov 's 1962 novel Pale Fire which are supposed to have been written by a poet, " John Shade ", who is actually fictional. As a joke, Gardner credited the lines only to Shade and put Shade's name in the index as if he were a real person. In his 1969 novel Ada or Ardor: A Family Chronicle, Nabokov returned the favor by having the character Van Veen "quote" the Gardner book along with the two lines of verse: