Actually the interpretation of \Box_E as its own proof system only requires the other systems to be finite extenions of PA, but I should mention that requirement! Nonetheless even if they’re not finite, everything still works because \Box_E still satisfies necessitation, distributivity, and existence of modal fixed points.
Actually the interpretation of \Box_E as its own proof system only requires the other systems to be finite extenions of PA, but I should mention that requirement! Nonetheless even if they’re not finite, everything still works because \Box_E still satisfies necessitation, distributivity, and existence of modal fixed points.
Thanks for bringing this up.