Effectively nowhere simple sets

1984 ◽  
Vol 49 (1) ◽  
pp. 129-136 ◽  
Author(s):  
D. Miller ◽  
J. B. Remmel
Keyword(s):  
Simple Proof ◽  
Recursive Function ◽  
Finite Sets ◽  
Definition Of ◽  
Simple Sets

An r.e. set A is nowhere simple if for every r.e. set We such that We − A is infinite, there is an infinite r.e. set W such that W ⊆ We − A. The definition of nowhere simple sets is due to R. Shore in [4]. In [4], Shore studied various properties of nowhere simple sets and showed that they could be used to give an elegant and simple proof of the fact that every nontrivial class of r.e. sets C closed under recursive isomorphisms is an automorphism base for , the lattice of r.e. sets modulo finite sets, (that is, an automorphism α of is completely determined by its action on C; see Theorem 8 of [4]). Shore also defined the notion of effectively nowhere simple sets.Definition. An r.e. set A is effectively nowhere simple if there is a recursive function f such that for every i, Wf(i) ⊆ Wi − A and Wf(i) is infinite iff Wi − A is infinite. f is called a witness function for A.Other than to produce examples of effectively nowhere simple sets and nowhere simple sets that are not effectively nowhere simple, Shore did not concern himself with the properties of effectively nowhere simple sets since he felt that effectively nowhere simple sets were unlikely to be lattice invariant in either E, the lattice of r.e. sets, or in .

Homology of the Fermat Tower and Universal Measures for Jacobi Sums

2016 ◽  
Vol 59 (3) ◽  
pp. 624-640
Author(s):  
Noriyuki Otsubo
Keyword(s):  
Power Series ◽  
Group Ring ◽  
Simple Proof ◽  
Homology Group ◽  
Interpolation Property ◽  
Cyclic Module ◽  
Precise Description ◽  
Fermat Curve ◽  
Jacobi Sums ◽  
Definition Of

AbstractWe give a precise description of the homology group of the Fermat curve as a cyclic module over a group ring. As an application, we prove the freeness of the profinite homology of the Fermat tower. This allows us to define measures, an equivalent of Anderson’s adelic beta functions, in a manner similar to Ihara’s definition of ℓ-adic universal power series for Jacobi sums. We give a simple proof of the interpolation property using a motivic decomposition of the Fermat curve.

Hyperhypersimple supersets in admissible recursion theory

1983 ◽  
Vol 48 (1) ◽  
pp. 185-192
Author(s):  
C. T. Chong
Keyword(s):  
Recursion Theory ◽  
Order Type ◽  
Complete Characterization ◽  
Point Of View ◽  
Extensive Literature ◽  
Careful Study ◽  
Finite Sets ◽  
Natural Class ◽  
Recursively Enumerable Set ◽  
Simple Sets

Let α be an admissible ordinal. An α-recursively enumerable set H is hyper-hypersimple (hh-simple) if its lattice of α-r.e. supersets forms a Boolean algebra. In [3], Chong and Lerman characterized the class ℋ() of hh-simple -r.e. sets as precisely those -r.e. sets whose complements are unbounded and of order type less than . Perhaps a nice example of such a set is {σ∣σ is not for any n < ω}. It follows that all hh-simple sets in are nonhyperregular and therefore of degree 0′. That ℋ() is a natural class to study can be seen from the role played by its ω-counterpart in the study of decision problems and automorphisms of ℰ*(ω), the lattice of ω-r.e. sets modulo finite sets (Soare [13] gives an extensive literature on these topics). In α-recursion theory the existence of hh-simple sets is not an all pervasive phenomenon, and there is as yet no complete characterization of the admissible ordinal α for which ℋ(α) is nonempty. While this situation is admittedly unsatisfactory, we feel that the lattice ℰ*(α) of α-r.e. sets modulo α*-finite sets for which ℋ(α) ≠ ∅ deserves a careful study. Indeed armed with some understanding over the last few years of the general theory of admissible ordinals, it is tempting to focus one's attention on some specific ordinals whose characteristics admit a more detailed analysis of the fine structure of sets and degrees. From this point of view, and ℋ() are natural objects of study since the former is a typical example of a non-Σ2-projectible, Σ2-inadmissible ordinal, while the latter is important for the investigations of automorphisms over ℰ*().

Minimal α-recursion theoretic degrees

1973 ◽  
Vol 38 (1) ◽  
pp. 18-28 ◽  
Author(s):  
John M. MacIntyre
Keyword(s):  
Recursive Function ◽  
Regular Cardinal ◽  
Recursion Theory ◽  
Minimal Degree ◽  
The Other ◽  
Ordinal Numbers ◽  
Definition Of

This paper investigates the problem of extending the recursion theoretic construction of a minimal degree to the Kripke [2]-Platek [5] recursion theory on the ordinals less than an admissible ordinal α, a theory derived from the Takeuti [11] notion of a recursive function on the ordinal numbers. As noted in Sacks [7] when one generalizes the recursion theoretic definition of relative recursiveness to α-recursion theory for α > ω the two usual definitions give rise to two different notions of reducibility. We will show that whenever α is either a countable admissible or a regular cardinal of the constructible universe there is a subset of α whose degree is minimal for both notions of reducibility. The result is an excellent example of a theorem of ordinary recursion theory obtainable via two different constructions, one of which generalizes, the other of which does not. The construction which cannot be lifted to α-recursion theory is that of Spector [10]. We sketch the reasons for this in §3.

scholarly journals On the Equivalence between Small-Step and Big-Step Abstract Machines: A Simple Application of Lightweight Fusion

2007 ◽  
Vol 14 (16) ◽  
Author(s):  
Olivier Danvy ◽  
Kevin Millikin
Keyword(s):  
Fixed Point ◽  
Simple Proof ◽  
Recursive Function ◽  
State Transition ◽  
Transition Function ◽  
Simple Application ◽  
Small Step ◽  
Final State ◽  
Abstract Machines ◽  
State Transition Function

We show how Ohori and Sasano's recent lightweight fusion by fixed-point promotion provides a simple way to prove the equivalence of the two standard styles of specification of abstract machines: (1) in small-step form, as a state-transition function together with a `driver loop,' i.e., a function implementing the iteration of this transition function; and (2) in big-step form, as a tail-recursive function that directly maps a given configuration to a final state, if any. The equivalence hinges on our observation that for abstract machines, fusing a small-step specification yields a big-step specification. We illustrate this observation here with a recognizer for Dyck words, the CEK machine, and Krivine's machine with call/cc.<br /> <br />The need for such a simple proof is motivated by our current work on small-step abstract machines as obtained by refocusing a function implementing a reduction semantics (a syntactic correspondence), and big-step abstract machines as obtained by CPS-transforming and then defunctionalizing a function implementing a big-step semantics (a functional correspondence).

Nowhere simple sets and the lattice of recursively enumerable sets

1978 ◽  
Vol 43 (2) ◽  
pp. 322-330 ◽  
Author(s):  
Richard A. Shore
Keyword(s):  
Boolean Algebra ◽  
Classification Scheme ◽  
Recursion Theory ◽  
Boolean Algebras ◽  
The Other ◽  
Finite Sets ◽  
Recursively Enumerable ◽  
Recursively Enumerable Sets ◽  
Simple Sets ◽  
Invariant Properties

Ever since Post [4] the structure of recursively enumerable sets and their classification has been an important area in recursion theory. It is also intimately connected with the study of the lattices and of r.e. sets and r.e. sets modulo finite sets respectively. (This lattice theoretic viewpoint was introduced by Myhill [3].) Key roles in both areas have been played by the lattice of r.e. supersets, , of an r.e. set A (along with the corresponding modulo finite sets) and more recently by the group of automorphisms of and . Thus for example we have Lachlan's deep result [1] that Post's notion of A being hyperhypersimple is equivalent to (or ) being a Boolean algebra. Indeed Lachlan even tells us which Boolean algebras appear as —precisely those with Σ3 representations. There are also many other simpler but still illuminating connections between the older typology of r.e. sets and their roles in the lattice . (r-maximal sets for example are just those with completely uncomplemented.) On the other hand, work on automorphisms by Martin and by Soare [8], [9] has shown that most other Post type conditions on r.e. sets such as hypersimplicity or creativeness which are not obviously lattice theoretic are in fact not invariant properties of .In general the program of analyzing and classifying r.e. sets has been directed at the simple sets. Thus the subtypes of simple sets studied abound — between ten and fifteen are mentioned in [5] and there are others — but there seems to be much less known about the nonsimple sets. The typologies introduced for the nonsimple sets begin with Post's notion of creativeness and add on a few variations. (See [5, §8.7] and the related exercises for some examples.) Although there is a classification scheme for r.e. sets along the simple to creative line (see [5, §8.7]) it is admitted to be somewhat artificial and arbitrary. Moreover there does not seem to have been much recent work on the nonsimple sets.

Finite algebras of relations are representable on finite sets

1999 ◽  
Vol 64 (1) ◽  
pp. 243-267 ◽  
Author(s):  
H. Andréka ◽  
I. Hodkinson ◽  
I. Németi
Keyword(s):  
Simple Proof ◽  
Finite Algebra ◽  
Finite Sets ◽  
Base Property ◽  
Finite Algebras ◽  
Relational Structures ◽  
Combinatorial Theorem ◽  
Finite Base ◽  
Algebras Of Relations ◽  
Finite Set

AbstractUsing a combinatorial theorem of Herwig on extending partial isomorphisms of relational structures, we give a simple proof that certain classes of algebras, including Crs, polyadic Crs, and WA, have the ‘finite base property’ and have decidable universal theories, and that any finite algebra in each class is representable on a finite set.

A simple proof of the chaoticity of shift map under a new definition of chaos

2011 ◽  
Vol 27 (4) ◽  
pp. 332-339
Author(s):  
Indranil Bhaumik ◽  
Binayak S. Choudhury ◽  
Basudeb Mukhopadhyay
Keyword(s):  
Simple Proof ◽  
Shift Map ◽  
Definition Of

Variations on promptly simple sets

1985 ◽  
Vol 50 (1) ◽  
pp. 138-148 ◽  
Author(s):  
Wolfgang Maass
Keyword(s):  
Recursive Function ◽  
Splitting Property ◽  
Recursively Enumerable ◽  
Recursively Enumerable Sets ◽  
Simple Sets

In this paper we answer the question of whether all low sets with the splitting property are promptly simple. Further we try to make the role of lowness properties and prompt simplicity in the construction of automorphisms of the lattice of r.e. (recursively enumerable) sets more perspicuous. It turns out that two new properties of r.e. sets, which are dual to each other, are essential in this context: the prompt and the low shrinking property.In an earlier paper [4] we had shown (using Soare's automorphism construction [10] and [12]) that all r.e. generic sets are automorphic in the lattice ℰ of r.e. sets under inclusion. We called a set A promptly simple if Ā is infinite and there is a recursive enumeration of A and the r.e. sets (We)e∈N such that if We is infinite then there is some element (or equivalently: infinitely many elements) x of We such that x gets into A “promptly” after its appearance in We (i.e. for some fixed total recursive function f we have x ∈ Af(s), where s is the stage at which x entered We). Prompt simplicity in combination with lowness turned out to capture those properties of r.e. generic sets that were used in the mentioned automorphism result. In a following paper with Shore and Stob [7] we studied an ℰ-definable consequence of prompt simplicity: the splitting property.

scholarly journals Only Two Letters: The Correspondence between Herbrand and Gödel

2005 ◽  
Vol 11 (2) ◽  
pp. 172-184 ◽  
Author(s):  
Wilfried Sieg
Keyword(s):  
Significant Role ◽  
Full Text ◽  
Recursive Function ◽  
Computability Theory ◽  
General Recursive Function ◽  
Kurt Gödel ◽  
Incompleteness Theorems ◽  
Potential Impact ◽  
Definition Of ◽  
Crucial Part

AbstractTwo young logicians, whose work had a dramatic impact on the direction of logic, exchanged two letters in early 1931. Jacques Herbrand initiated the correspondence on 7 April and Kurt Gödel responded on 25 July, just two days before Herbrand died in a mountaineering accident at La Bérarde (Isère). Herbrand's letter played a significant role in the development of computability theory. Gödel asserted in his 1934 Princeton Lectures and on later occasions that it suggested to him a crucial part of the definition of a general recursive function. Understanding this role in detail is of great interest as the notion is absolutely central. The full text of the letter had not been available until recently, and its content (as reported by Gödel) was not in accord with Herbrand's contemporaneous published work. Together, the letters reflect broader intellectual currents of the time: they are intimately linked to the discussion of the incompleteness theorems and their potential impact on Hilbert's Program.

scholarly journals A Note on Stirling's Theorem

1933 ◽  
Vol 28 ◽  
pp. xii-xiii
Author(s):  
J. R. Wilton
Keyword(s):  
Simple Proof ◽  
Definition Of ◽  
Image Position

Let Γ(1 + x) = √(2πx)xxe–x φ(x);This result is Stirling's theorem. A simple proof is given in § 1.87 of Titchmarsh's Theory of Functions (Oxford Univ. Press, 1932).Rather more than Stirling's theorem can be proved by a method which assumes nothing but the definition of the Γ-function, and Γ (½) = √π, from which it follows that

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