1. Anderson, C. A. (1989). Russellian intensional logic. In J. Almog, J. Perry, & H. Wettstein (Eds.), Themes from Kaplan (pp. 67–103). New York: Oxford University Press.
2. Anderson, D. J., & Zalta, E. (2004). Frege, boolos, and logical objects. Journal of Philosophical Logic, 33(1), 1–26.
3. Boolos, G. (1987). The Consistency of Frege's Foundations of Arithmetic. In J. Thomson (Ed.), On being and saying. Cambridge: MIT Press
4. reprinted in Boolos, G. (1998) J. Burgess & R. Jeffrey (Eds.), Logic, logic, and logic (pp. 183-201). Cambridge: Harvard University Press.
5. Bueno, O., Menzel, C., & E. Zalta, (2014). Worlds and propositions set free. Erkenntnis, 79, 797–820.