Karen Elizabeth Gordon (1993). “The New Well-tempered Sentence: A Punctuation Handbook for the Innocent, the Eager, and the Doomed”, p.15, Houghton Mifflin Harcourt
Karen Elizabeth Gordon (1993). “The New Well-tempered Sentence: A Punctuation Handbook for the Innocent, the Eager, and the Doomed”, p.22, Houghton Mifflin Harcourt