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2

D. K. Brown, Functional Analysis in Weak Subsystems of Second Order Arithmetic, Ph. D. Thesis, Pennsylvania State University, 1987, vii + 150 pages.

3

D. K. Brown and S. G. Simpson, Which set existence axioms are needed to prove the separable Hahn-Banach theorem?, Annals of Pure and Applied Logic, 31, 1986, pp. 123-144.

4

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5

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6

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7

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8

H. Friedman, S. G. Simpson and R. L. Smith, Countable algebra and set existence axioms, Annals of Pure and Applied Logic, 25, 1983, pp. 141-181.

9

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10

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11

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12

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13

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14

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15

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16

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17

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18

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19

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20

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21

S. G. Simpson, Which set existence axioms are needed to prove the Cauchy/Peano theorem for ordinary differential equations?, Journal of Symbolic Logic, 49, 1984, pp. 783-802.

22

S. G. Simpson, Friedman's research on subsystems of second order arithmetic, in: Harvey Friedman's Research in the Foundations of Mathematics, edited by L. Harrington, M. Morley, A. Scedrov and S. G. Simpson, North-Holland, 1985, pp. 137-159.

23

S. G. Simpson, Subsystems of Z₂ and Reverse Mathematics, appendix to: G. Takeuti, Proof Theory, 2nd edition, North-Holland, 1986, pp. 434-448.

24

S. G. Simpson, Subsystems of Second Order Arithmetic, in preparation

25

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26

G. Takeuti, Recent topics on proof theory (in Japanese), Journal of the Japan Association for Philosophy of Science, 17, 1984, pp. 1-5.

27

J. van Heijenoort (editor), From Frege to Gödel: A Source Book in Mathematical Logic, 1879-1931, Harvard University Press, 1967, xii + 660 pages.

28

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