Bibliography

1

Harvey Friedman.
Bar induction and $\Pi^1_1$- $\mathsf{CA}$.
Journal of Symbolic Logic, 34:353-362, 1969.

2

Harvey Friedman.
Subsystems of second order arithmetic and their use in the formalization of mathematics.
19 pages, unpublished, March 1974.

3

Harvey Friedman.
Some systems of second order arithmetic and their use.
In Proceedings of the International Congress of Mathematicians, Vancouver 1974, volume 1, pages 235-242. Canadian Mathematical Congress, 1975.

4

Gerald E. Sacks.
Higher Recursion Theory.
Perspectives in Mathematical Logic. Springer-Verlag, 1990.
XV + 344 pages.

5

Stephen G. Simpson.
Subsystems of Second Order Arithmetic.
Perspectives in Mathematical Logic. Springer-Verlag, 1999.
XIV + 445 pages.

6

Stephen G. Simpson.
$\Pi^0_1$ sets and models of $\mathsf{WKL}_0$.
April 2000.
Preprint, 26 pages, to appear.

7

Stephen G. Simpson, Kazuyuki Tanaka, and Takeshi Yamazaki.
Some conservation results for weak König's lemma.
February 2000.
Preprint, 26 pages, to appear.