The structure of the poem is also quite complex, with mathematical and numerological patterns distributed throughout the work, particularly threes and nines. The poem is often lauded for its particularly human qualities: Dante's skillful delineation of the characters he encounters in Hell, Purgatory, and Paradise; his bitter denunciations of Florentine and Italian politics; and his powerful poetic imagination. Dante's use of real characters, according to Dorothy Sayers in her introduction to her translation of the "Inferno", allows Dante the freedom of not having to involve the reader in description, and allows him to " room in his poem for the discussion of a great many subjects of the utmost importance, thus widening its range and increasing its variety."