S. Feferman et G. Jager, SYSTEMS OF EXPLICIT MATHEMATICS WITH NONCONSTRUCTIVE MU-OPERATOR .1, Annals of pure and applied Logic, 65(3), 1993, pp. 243-263
This paper is mainly concerned with the proof-theoretic analysis of sy
stems of explicit mathematics with a non-constructive minimum operator
. We start off from a basic theory BON of operators and numbers and ad
d some principles of set and formula induction on the natural numbers
as well as axioms for mu. The principal results then state: (i) BON(mu
) plus set induction is proof-theoretically equivalent to Peano arithm
etic PA; (ii) BON(mu) plus formula induction is proof-theoretically eq
uivalent to the system (IIinfinity0-CA)(<epsilon 0) of second-order ar
ithmetic.