Published online by Cambridge University Press: 12 March 2014
In [1], Bemays gives an axiomatization of set-theory which represents the furthest development to date of the Zermelo-Frankel-Gödel tradition. The purpose of this note is to show that one of his axioms is redundant.
Primitives are ∈, set-abstraction (denoted [x/A(x)]) and the Hilbert selector (denoted σ). Different styles are used for free variables (a, b,c, …) and bound variables (x, y, z, …); both kinds of variables range over both sets and classes. Quantifiers and connectives are classical.