In metrical poems, neck couplets and parallel couplets are antithetical sentences. That is to say, in rhyme, the second paragraph and the third paragraph are antithetical sentences.
Definition of Duality Sentence: Duality is a rhetorical way to express two opposite or similar meanings with a pair of phrases or sentences with the same number of words, the same structural form and symmetrical meaning. Duality is mainly from the structural form, which requires the structure to be commensurate and the number of words to be equal.