Positive set theory is at present a subject on its own, from the initial work of R.J. Malitz [16], to the further developments including topological models [6], [7], and very strong variants, in particular Esser’s theory GPK ∞ where the class of all well-founded sets interprets ZF [3], [4]. In another direction, namely in languages allowing terms, does positive set theory appear as a weakening ...