1. Dodgson, C. L. 1885.Supplement to Euclid and his Modern Rivals: Containing a Notice of Henrici's Geometry Together with Selections from the Reviews. MacMillan: London, p. 351.
2. MacColl, H. 1906.Symbolic Logic and its Applications, London: Longmans, Green & Co., pp. 78–80.
3. Hugh Maccoll and the Birth of Logical Pluralism