Humberstone asks whether every theorem of BCI provably implies for some formula . Meyer conjectures that the axiom does not imply any such "self-implication." We prove a slightly stronger result, thereby confirming Meyer's conjecture.
"Self-implications in BCI." Notre Dame J. Formal Logic 49 (3) 295 - 305, 2008. https://doi.org/10.1215/00294527-2008-013