 Boolos was interested in GST only as a fragment of Z that is just powerful enough to interpret Peano arithmetic.He never lingered over GST, only mentioning it briefly in several papers discussing the systems of Frege's "Grundlagen" and "Grundgesetze", and how they could be modified to eliminate Russell's paradox.The system Aξ'[δ0] in Tarski and Givant (1987