1. Cantor, ‘Ein Beitrag zur Mannigfaltigkeitslehre’, Journ. für die Reine and Angewandte Math. 84 (1878), 242–258.
2. The phrase, though not the view, is J. L. Austin’s. See Sense and Sensibilia, Oxford, 1962, p. 8.
3. Kuratowski, Topology,Volume I, New York and London, 1966, p.75. A common alternative is ‘regular open set’.
4. Compare Halmos, Lectures on Boolean Algebras, Princeton, N.J., 1963, p. 14.
5. The identification of receptacles with non-null open domains was suggested to me by remarks made by Tarski in ‘Foundations of the Geometry of Solids’, included in his Logic, Semantics, and Metamathematics,Oxford, 1956, pp. 24–29.