Published online by Cambridge University Press: 12 March 2014
The starting point of this article is an old question asked by Feferman in his paper on Hancock's conjecture [6] about the strength of . This theory is obtained from the well-known theory ID1 by restricting fixed point induction to formulas that contain fixed point constants only positively. The techniques used to perform the proof-theoretic analysis of
also permit to analyze its transfinitely iterated variants
. Thus, we eventually know that