On the relation between choice and comprehension principles in second order arithmetic
Andrea Cantini · Journal of Symbolic Logic · 1986
Abstract We give a new elementary proof of the comparison theorem relating and ; the proof does not use Skolem theories. By the same method we prove: a) , for suitable classes of sentences; b) proves the consistency of , for finitek, and hence is stronger than . a) and b) answer a question of Feferman and Sieg.