Yorke also took phrases from Dante's "Inferno", the subject of his partner Rachel Owen's PhD thesis. Several songs, such as "2 + 2 = 5", "Sit Down Stand Up", and "Sail to the Moon", reference Christian versions of good and evil and heaven and hell, a first for Radiohead's music. Other songs reference science fiction, horror and fantasy, such as the wolves and vampires of "A Wolf at the Door" and "We Suck Young Blood", the reference to the "2 + 2 = 5" slogan in the dystopian novel "Nineteen Eighty-Four", and the allusion to the giant of "Gulliver's Travels" in "Go to Sleep".