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2. Boolos, G. (1998). Logic, Logic, and Logic, Harvard University Press, Cambridge, MA.
3. Boolos, G. (1987). The consistency of Frege's 'Foundations of Arithmetic', in J. Thomson (ed.), On Being and Saying, MIT Press, Cambridge, MA; reprinted in Boolos (1998, pp. 183-201). [Page references are given as 'n/m', where n is a page number (range) in the original and m is the corresponding page number (range) in the reprint.]
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5. Burgess, J. (forthcoming). On a consistent subsystem of Frege's Grundgesetze, Notre Dame J. Formal Logic.