1. P. Aczel, Frege structures and the notions of proposition, truth and set, in The Kleene Symposium, ed. by J. Barwise, H.J. Keisler, K. Kunen (North Holland, Amsterdam, 1980), pp. 31–59
2. J. Burgess, Friedman and the axiomatization of Kripke’s theory of truth, in Foundational Adventures: Essays in Honor of Harvey M. Friedman, ed by N. Tennant (College Publications, London, 2014), pp. 125–148
3. A. Cantini, Levels of implications and type free theories of partial classifications with approximation operator. Zeitschrift f. Math. Logik u. Grundlagen 38, 107–141 (1992)
4. A. Cantini, P. Minari, Uniform inseparability in explicit mathematics. J. Symbolic Logic 61, 313–326 (1999)
5. A. Cantini, On a Russellian paradox about propositions and truth, in One Hundred Years of Russell’s Paradox. Mathematics, Logic and Philosophy ed by G. Link (Walter de Gruyter, Berlin, 2004), pp. 259–284