The role of parameters in bar rule and bar induction
Michael Rathjen · Journal of Symbolic Logic · 1991
Abstract For several subsystems of second order arithmeticTwe show that the proof-theoretic strength ofT+ (bar rule) can be characterized in terms ofT+ (bar induction)□, where the latter scheme arises from the scheme of bar induction by restricting it to well-orderings with no parameters. In addition, we demonstrate that ,ACA0+ (bar rule) andACA0+ (bar induction)□prove the same -sentences.