2,800 research outputs found
Partition genericity and pigeonhole basis theorems
There exist two notions of typicality in computability theory, namely,
genericity and randomness. In this article, we introduce a new notion of
genericity, called partition genericity, which is at the intersection of these
two notions of typicality, and show that many basis theorems apply to partition
genericity. More precisely, we prove that every co-hyperimmune set and every
Kurtz random is partition generic, and that every partition generic set admits
weak infinite subsets. In particular, we answer a question of Kjos-Hanssen and
Liu by showing that every Kurtz random admits an infinite subset which does not
compute any set of positive Hausdorff dimension. Partition genericty is a
partition regular notion, so these results imply many existing pigeonhole basis
theorems.Comment: 23 page
Computable Jordan Decomposition of Linear Continuous Functionals on
By the Riesz representation theorem using the Riemann-Stieltjes integral,
linear continuous functionals on the set of continuous functions from the unit
interval into the reals can either be characterized by functions of bounded
variation from the unit interval into the reals, or by signed measures on the
Borel-subsets. Each of these objects has an (even minimal) Jordan decomposition
into non-negative or non-decreasing objects. Using the representation approach
to computable analysis, a computable version of the Riesz representation
theorem has been proved by Jafarikhah, Lu and Weihrauch. In this article we
extend this result. We study the computable relation between three Banach
spaces, the space of linear continuous functionals with operator norm, the
space of (normalized) functions of bounded variation with total variation norm,
and the space of bounded signed Borel measures with variation norm. We
introduce natural representations for defining computability. We prove that the
canonical linear bijections between these spaces and their inverses are
computable. We also prove that Jordan decomposition is computable on each of
these spaces
On the mathematical and foundational significance of the uncountable
We study the logical and computational properties of basic theorems of
uncountable mathematics, including the Cousin and Lindel\"of lemma published in
1895 and 1903. Historically, these lemmas were among the first formulations of
open-cover compactness and the Lindel\"of property, respectively. These notions
are of great conceptual importance: the former is commonly viewed as a way of
treating uncountable sets like e.g. as 'almost finite', while the
latter allows one to treat uncountable sets like e.g. as 'almost
countable'. This reduction of the uncountable to the finite/countable turns out
to have a considerable logical and computational cost: we show that the
aforementioned lemmas, and many related theorems, are extremely hard to prove,
while the associated sub-covers are extremely hard to compute. Indeed, in terms
of the standard scale (based on comprehension axioms), a proof of these lemmas
requires at least the full extent of second-order arithmetic, a system
originating from Hilbert-Bernays' Grundlagen der Mathematik. This observation
has far-reaching implications for the Grundlagen's spiritual successor, the
program of Reverse Mathematics, and the associated G\"odel hierachy. We also
show that the Cousin lemma is essential for the development of the gauge
integral, a generalisation of the Lebesgue and improper Riemann integrals that
also uniquely provides a direct formalisation of Feynman's path integral.Comment: 35 pages with one figure. The content of this version extends the
published version in that Sections 3.3.4 and 3.4 below are new. Small
corrections/additions have also been made to reflect new development
Uniformity, Universality, and Computability Theory
We prove a number of results motivated by global questions of uniformity in
computability theory, and universality of countable Borel equivalence
relations. Our main technical tool is a game for constructing functions on free
products of countable groups.
We begin by investigating the notion of uniform universality, first proposed
by Montalb\'an, Reimann and Slaman. This notion is a strengthened form of a
countable Borel equivalence relation being universal, which we conjecture is
equivalent to the usual notion. With this additional uniformity hypothesis, we
can answer many questions concerning how countable groups, probability
measures, the subset relation, and increasing unions interact with
universality. For many natural classes of countable Borel equivalence
relations, we can also classify exactly which are uniformly universal.
We also show the existence of refinements of Martin's ultrafilter on Turing
invariant Borel sets to the invariant Borel sets of equivalence relations that
are much finer than Turing equivalence. For example, we construct such an
ultrafilter for the orbit equivalence relation of the shift action of the free
group on countably many generators. These ultrafilters imply a number of
structural properties for these equivalence relations.Comment: 61 Page
The proof-theoretic strength of Ramsey's theorem for pairs and two colors
Ramsey's theorem for -tuples and -colors () asserts
that every k-coloring of admits an infinite monochromatic
subset. We study the proof-theoretic strength of Ramsey's theorem for pairs and
two colors, namely, the set of its consequences, and show that
is conservative over . This
strengthens the proof of Chong, Slaman and Yang that does not
imply , and shows that is
finitistically reducible, in the sense of Simpson's partial realization of
Hilbert's Program. Moreover, we develop general tools to simplify the proofs of
-conservation theorems.Comment: 32 page
Set Theory or Higher Order Logic to Represent Auction Concepts in Isabelle?
When faced with the question of how to represent properties in a formal proof
system any user has to make design decisions. We have proved three of the
theorems from Maskin's 2004 survey article on Auction Theory using the
Isabelle/HOL system, and we have produced verified code for combinatorial
Vickrey auctions. A fundamental question in this was how to represent some
basic concepts: since set theory is available inside Isabelle/HOL, when
introducing new definitions there is often the issue of balancing the amount of
set-theoretical objects and of objects expressed using entities which are more
typical of higher order logic such as functions or lists. Likewise, a user has
often to answer the question whether to use a constructive or a
non-constructive definition. Such decisions have consequences for the proof
development and the usability of the formalization. For instance, sets are
usually closer to the representation that economists would use and recognize,
while the other objects are closer to the extraction of computational content.
In this paper we give examples of the advantages and disadvantages for these
approaches and their relationships. In addition, we present the corresponding
Isabelle library of definitions and theorems, most prominently those dealing
with relations and quotients.Comment: Preprint of a paper accepted for the forthcoming CICM 2014 conference
(cicm-conference.org/2014): S.M. Watt et al. (Eds.): CICM 2014, LNAI 8543,
Springer International Publishing Switzerland 2014. 16 pages, 1 figur
"Weak yet strong'' restrictions of Hindman's Finite Sums Theorem
We present a natural restriction of Hindman’s Finite Sums Theorem that admits a simple combinatorial proof (one that does not also prove the full Finite Sums Theorem) and low computability-theoretic and proof-theoretic upper bounds, yet implies the existence of the Turing Jump, thus realizing the only known lower bound for the full Finite Sums Theorem. This is the first example of this kind. In fact we isolate a rich family of similar restrictions of Hindman’s Theorem with analogous propertie
Coloring trees in reverse mathematics
The tree theorem for pairs (), first introduced by Chubb,
Hirst, and McNicholl, asserts that given a finite coloring of pairs of
comparable nodes in the full binary tree , there is a set of nodes
isomorphic to which is homogeneous for the coloring. This is a
generalization of the more familiar Ramsey's theorem for pairs
(), which has been studied extensively in computability theory
and reverse mathematics. We answer a longstanding open question about the
strength of , by showing that this principle does not imply
the arithmetic comprehension axiom () over the base system,
recursive comprehension axiom (), of second-order arithmetic.
In addition, we give a new and self-contained proof of a recent result of Patey
that is strictly stronger than . Combined,
these results establish as the first known example of a
natural combinatorial principle to occupy the interval strictly between
and . The proof of this fact uses an
extension of the bushy tree forcing method, and develops new techniques for
dealing with combinatorial statements formulated on trees, rather than on
.Comment: 25 page
Computability of entropy and information in classical Hamiltonian systems
We consider the computability of entropy and information in classical
Hamiltonian systems. We define the information part and total information
capacity part of entropy in classical Hamiltonian systems using relative
information under a computable discrete partition.
Using a recursively enumerable nonrecursive set it is shown that even though
the initial probability distribution, entropy, Hamiltonian and its partial
derivatives are computable under a computable partition, the time evolution of
its information capacity under the original partition can grow faster than any
recursive function. This implies that even though the probability measure and
information are conserved in classical Hamiltonian time evolution we might not
actually compute the information with respect to the original computable
partition
"Weak yet strong" restrictions of Hindman's Finite Sums Theorem
We present a natural restriction of Hindman's Finite Sums Theorem that admits
a simple combinatorial proof (one that does not also prove the full Finite Sums
Theorem) and low computability-theoretic and proof-theoretic upper bounds, yet
implies the existence of the Turing Jump, thus realizing the only known lower
bound for the full Finite Sums Theorem. This is the first example of this kind.
In fact we isolate a rich family of similar restrictions of Hindman's Theorem
with analogous properties
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