Axiom schema of Markov s principle preserves disjunction and existence properties

Transcription

1 Axiom schema of Markov s principle preserves disjunction and existence properties Nobu-Yuki Suzuki Shizuoka University Computability Theory and Foundations of Mathematics 2015 September 7, 2015 (Tokyo, Japan) N-Y Suzuki (Shizuoka Univ) Markov s principle preserves DP and EP CTFM 2015 (Sept 7, 2015) 1 / 11

2 Introduction: Disjunction and Existence Properties Hallmarks of constructivity of intuitionistic logic H : Fact H has the disjunction property (DP); for every A B: H A B H A or H B H has the existence property (EP); for every xa(x): H xa(x) there exists a v such that H A(v) NB A(v) should be taken as a formula congruent to A free from collision of variables N-Y Suzuki (Shizuoka Univ) Markov s principle preserves DP and EP CTFM 2015 (Sept 7, 2015) 2 / 11

3 Introduction: Disjunction and Existence Properties Hallmarks of constructivity of intuitionistic logic H : Fact H has the disjunction property (DP); for every A B: H A B H A or H B H has the existence property (EP); for every xa(x): H xa(x) there exists a v such that H A(v) H + A: the logic obtained from H by adding the axiom schema A There are schmemata A such that H + A enjoys both of DP and EP We are interested in such schemata (ie, H + A still enjoys DP and EP) in the setting of Intermediate Predicate Logics, particularly in those schemata related to constructive theories NB A(v) should be taken as a formula congruent to A free from collision of variables N-Y Suzuki (Shizuoka Univ) Markov s principle preserves DP and EP CTFM 2015 (Sept 7, 2015) 2 / 11

4 Markov s Principle and Limited Principle of Omniscience In the setting of intermediate Predicate Logics, we consider: Axiom schema of Markov s principle: MP : x(a(x) A(x)) xa(x) xa(x) Axiom schema of the limited principle of omniscience: LPO : x(a(x) A(x)) xa(x) xa(x), Both principles enlarge the concept of constructivity, particularly the concept of from that of intuitionistic logic H However, still we have: Theorem H + MP and H + LPO enjoy DP and EP That is, MP and LPO preserve DP and EP N-Y Suzuki (Shizuoka Univ) Markov s principle preserves DP and EP CTFM 2015 (Sept 7, 2015) 3 / 11

5 Harrop-DP and Harrop-EP Definition A formula is said to be a Harrop-formula (H-formula) if every strictly positive subformula is neither of the form A B nor xa(x) Theorem (Harrop) H has the H(arrop)-DP and the H(arrop)-EP, ie, for any H-formula H, H H A B H H A or H H B, H H xa(x) H H A(v) for some v Theorem H + MP and H + LPO enjoy H-DP and H-EP That is, MP and LPO preserve H-DP and H-EP N-Y Suzuki (Shizuoka Univ) Markov s principle preserves DP and EP CTFM 2015 (Sept 7, 2015) 4 / 11

6 Pointed Join of Kripke Models Definition M 1, M 2 : Kripke frames with the least elements 0 1 and 0 2, resp, such that the domains at 0 1 and 0 2 coincide with V (= D 1 (0 1 ) = D 2 (0 2 )) A Kripke frame M is said to be the pointed join frame of M 1 and M 2, if M = {(0, V )} M 1 M 2 with a fresh least element 0 (M 1, = 1 ), (M 2, = 2 ): Kripke models with V = D 1 (0 1 ) = D 2 (0 2 ) A Kripke model (M, =) is said to be a pointed join model of (M 1, = 1 ) and (M 2, = 2 ), if M is the pointed join frame of M 1 and M 2, and the restrictions of = to M 1 and M 2 are = 1 and = 2, resp N-Y Suzuki (Shizuoka Univ) Markov s principle preserves DP and EP CTFM 2015 (Sept 7, 2015) 5 / 11

7 Axiomatic Truth and its Preservation Definition A formula A is said to be axiomatically true in a Kripke model (M, =), if universal closures of all of substitution instances of A are true in (M, =) Lemma If A preserves its axiomatic truth in the construction of pointed join models, ie, satisfies the following: If A is axiomatically true in Kripke models (M 1, = 1 ) and (M 2, = 2 ) with V = D 1 (0 1 ) = D 2 (0 2 ), then A is still axiomatically true in any pointed join model of (M 1, = 1 ) and (M 2, = 2 ), then H + A preserves H-DP and H-EP N-Y Suzuki (Shizuoka Univ) Markov s principle preserves DP and EP CTFM 2015 (Sept 7, 2015) 6 / 11

8 Axiomatic Truth and its Preservation Definition A formula A is said to be axiomatically true in a Kripke model (M, =), if universal closures of all of substitution instances of A are true in (M, =) Lemma If A preserves its axiomatic truth in the construction of pointed join models, ie, satisfies the following: If A is axiomatically true in Kripke models (M 1, = 1 ) and (M 2, = 2 ) with V = D 1 (0 1 ) = D 2 (0 2 ), then A is still axiomatically true in any pointed join model of (M 1, = 1 ) and (M 2, = 2 ), then H + A preserves H-DP and H-EP Theorem MP and LPO have this property Hence, MP and LPO preserve H-DP and H-EP N-Y Suzuki (Shizuoka Univ) Markov s principle preserves DP and EP CTFM 2015 (Sept 7, 2015) 6 / 11

9 Another Phenomenon: Prawitz-Doorman EP Definition A formula is said to be a weak Harrop-formula (wh-formula) if every strictly positive subformula is not of the form xa(x) Theorem (Prawitz, Doorman) H has the Prawitz-Doorman EP, ie, for any wh-formula H, H H xa(x) there exist finitely many v 1,, v n in the vocabulary of H xa(x) such that H H A(v 1 ) A(v n ) Prawitz proved EP of H by showing DP and the Prawitz-Doorman EP N-Y Suzuki (Shizuoka Univ) Markov s principle preserves DP and EP CTFM 2015 (Sept 7, 2015) 7 / 11

10 Another Phenomenon: Prawitz-Doorman EP Definition A formula is said to be a weak Harrop-formula (wh-formula) if every strictly positive subformula is not of the form xa(x) Theorem (Prawitz, Doorman) H has the Prawitz-Doorman EP, ie, for any wh-formula H, H H xa(x) there exist finitely many v 1,, v n in the vocabulary of H xa(x) such that H H A(v 1 ) A(v n ) Prawitz proved EP of H by showing DP and the Prawitz-Doorman EP Proposition H + MP and H + LPO fail to have the Prawitz-Doorman EP That is, MP and LPO do not preserve the Prawitz-Doorman EP N-Y Suzuki (Shizuoka Univ) Markov s principle preserves DP and EP CTFM 2015 (Sept 7, 2015) 7 / 11

11 Concluding Remarks (1) In this talk, we considered preservation of DP and EP by two schemata MP and LPO in the setting of intermediate predicate logics H-DP,H-EP PD-EP H YES YES H + MP, H + LPO YES NO N-Y Suzuki (Shizuoka Univ) Markov s principle preserves DP and EP CTFM 2015 (Sept 7, 2015) 8 / 11

12 Concluding Remarks (1) In this talk, we considered preservation of DP and EP by two schemata MP and LPO in the setting of intermediate predicate logics H-DP,H-EP PD-EP H YES YES H + MP, H + LPO YES NO H + WLPO, H + LLPO? YES H + CD YES NO H + WEM NO YES WLPO: x(p(x) p(x)) xp(x) xp(x), LLPO: { x(p(x) p(x)) x(q(x) q(x)) ( xp(x) xq(x)) } xp(x) xq(x), CD: x(p(x) q) xp(x) q, (x is not free in q) WEM: p p, N-Y Suzuki (Shizuoka Univ) Markov s principle preserves DP and EP CTFM 2015 (Sept 7, 2015) 8 / 11

13 Background Story: Ono s Problem P52 Relations betwen DP and EP in Intermediate Logics Relations? In intermediate predicate logics: DP EP? EP DP? (Nakamura 1983) There exists an intermediate logic having DP but lacking EP Ie, DP EP EP DP? in intermediate logics Ono s Problem P52 (1987) (cf Umezawa(1980), Minari(1983)) N-Y Suzuki (Shizuoka Univ) Markov s principle preserves DP and EP CTFM 2015 (Sept 7, 2015) 9 / 11

14 Background Story: Ono s Problem P52 Relations betwen DP and EP in Intermediate Logics Proposition In intermediate predicate logics, EP and DP are independent Ie, (Nakamura 1983) There exists an intermediate logic having DP but lacking EP Ie, DP EP (S ) There exists an intermediate logic having EP but lacking DP Ie, EP DP Theorem (S ) If L is closed under the rule: A (p(x) p(y)) (ZR) A where x, y and p are distinct and do not occur in A Then, EP of L implies DP of L N-Y Suzuki (Shizuoka Univ) Markov s principle preserves DP and EP CTFM 2015 (Sept 7, 2015) 9 / 11

15 Concluding Remarks (2) Do H + WLPO and H + LLPO have H-DP and/or H-EP? H-DP DP? H-EP EP? This problem is known as Ono s problem P54 Remark: In intermediate propositional logic, we have: H-DP DP There must be waiting us other axiom schemata arising from constructive theories which are interesting from the viewpoint of intermediate logics! There must be waiting us other phenomena in intermediate logics which are interesting from the view point of constructive theories! N-Y Suzuki (Shizuoka Univ) Markov s principle preserves DP and EP CTFM 2015 (Sept 7, 2015) 10 / 11

16 References Doorman, L M, A note on the existence property for intuitionistic logic with function symbols, Zeitschrift für Mathematische Logik und Grundlagen der Mathematik 36(1990), Gabbay, D, and de Jongh, D H, Sequences of decidable and finitely axiomatizable intermediate logics with the disjunction property, J Symbolic Logic 39(1974), Kleene, S C, Disjunction and existence under implication in elementary intuitionistic formalisms, J Symbolic Logic 27(1962), (An addendum, 28(1963), ) Komori, Y, Some results on the super-intuitionistic predicate logics, Reports on Mathematical Logic, No15(1983), Nakamura, T, Disjunction property for some intermediate predicate logics, ibid, Ono, H, Some problems in intermediate predicate logics, ibid, No21(1987), Prawitz, D, Natural deduction A proof-theoretical study, Acta Universitatis Stockholmiensis Stockholm Studies in Philosophy, No 3 Almqvist & Wiksell, Stockholm 1965 (Reprint: Dover Publications, 2006) Suzuki, N-Y, A remark on the delta operation and the Kripke sheaf semantics in super-intuitionistic predicate logics, Bulletin of Section of Logic, University of Lódź, 25(1996), Suzuki, N-Y, A negative solution to Ono s problem P52: Existence and disjunction properties in intermediate predicate Logics, to appear Troelstra, A S, Metamathematical investigation of intuitionistic arithmetic and analysis, Lecture Notes in Mathematics, Vol 344 (1973) N-Y Suzuki (Shizuoka Univ) Markov s principle preserves DP and EP CTFM 2015 (Sept 7, 2015) 11 / 11