C. Fermüller:
"Comments on Vagueness: A Mathematicians's Perspective by Thomas Vetterlein";
in: "Understanding Vagueness. Logical, Philosophical and Linguistic Perspectives", P. Cintula, C. Fermüller et al. (ed.); College Publications, London, 2011, ISBN: 978-1-84890-037-0, 87 - 90.