Tomasz Gizbert-Studnicki, Types of Vagueness, in: W. Krawietz, R. S. Summers, O. Weinberger, G. H. von Wright (eds.), The Reasonable as Rational. On Legal Argumentation and Justification, Duncker & Humblot, Berlin, 2000, pp. 135-144. Available at: <https://www.academia.edu/3373482/Types_of_Vagueness>