24,540 research outputs found
Thermodynamic Formalism for Topological Markov Chains on Borel Standard Spaces
We develop a Thermodynamic Formalism for bounded continuous potentials
defined on the sequence space , where is a general
Borel standard space. In particular, we introduce meaningful concepts of
entropy and pressure for shifts acting on and obtain the existence of
equilibrium states as additive probability measures for any bounded continuous
potential. Furthermore, we establish convexity and other structural properties
of the set of equilibrium states, prove a version of the
Perron-Frobenius-Ruelle theorem under additional assumptions on the regularity
of the potential and show that the Yosida-Hewitt decomposition of these
equilibrium states do not have a purely additive part.
We then apply our results to the construction of invariant measures of
time-homogeneous Markov chains taking values on a general Borel standard space
and obtain exponential asymptotic stability for a class of Markov operators. We
also construct conformal measures for an infinite collection of interacting
random paths which are associated to a potential depending on infinitely many
coordinates. Under an additional differentiability hypothesis, we show how this
process is related after a proper scaling limit to a certain infinite
dimensional diffusion.Comment: Accepted for publication in Discrete and Continuous Dynamical
Systems. 23 page
KT and HKT Geometries in Strings and in Black Hole Moduli Spaces
Some selected applications of KT and HKT geometries in string theory,
supergravity, black hole moduli spaces and hermitian geometry are reviewed. It
is shown that the moduli spaces of a large class of five-dimensional
supersymmetric black holes are HKT spaces. In hermitian geometry, it is shown
that a compact, conformally balanced, strong KT manifold whose associated KT
connection has holonomy contained in SU(n) is Calabi-Yau. The implication of
this result in the context of some string compactifications is explained.Comment: 26 pages, Contribution to the Proceedings of the Bonn workshop on
"Special Geometric Structures in String Theory", a change in terminology and
some other minor change
Formalising the pi-calculus using nominal logic
We formalise the pi-calculus using the nominal datatype package, based on
ideas from the nominal logic by Pitts et al., and demonstrate an implementation
in Isabelle/HOL. The purpose is to derive powerful induction rules for the
semantics in order to conduct machine checkable proofs, closely following the
intuitive arguments found in manual proofs. In this way we have covered many of
the standard theorems of bisimulation equivalence and congruence, both late and
early, and both strong and weak in a uniform manner. We thus provide one of the
most extensive formalisations of a process calculus ever done inside a theorem
prover.
A significant gain in our formulation is that agents are identified up to
alpha-equivalence, thereby greatly reducing the arguments about bound names.
This is a normal strategy for manual proofs about the pi-calculus, but that
kind of hand waving has previously been difficult to incorporate smoothly in an
interactive theorem prover. We show how the nominal logic formalism and its
support in Isabelle accomplishes this and thus significantly reduces the tedium
of conducting completely formal proofs. This improves on previous work using
weak higher order abstract syntax since we do not need extra assumptions to
filter out exotic terms and can keep all arguments within a familiar
first-order logic.Comment: 36 pages, 3 figure
Learning-assisted Theorem Proving with Millions of Lemmas
Large formal mathematical libraries consist of millions of atomic inference
steps that give rise to a corresponding number of proved statements (lemmas).
Analogously to the informal mathematical practice, only a tiny fraction of such
statements is named and re-used in later proofs by formal mathematicians. In
this work, we suggest and implement criteria defining the estimated usefulness
of the HOL Light lemmas for proving further theorems. We use these criteria to
mine the large inference graph of the lemmas in the HOL Light and Flyspeck
libraries, adding up to millions of the best lemmas to the pool of statements
that can be re-used in later proofs. We show that in combination with
learning-based relevance filtering, such methods significantly strengthen
automated theorem proving of new conjectures over large formal mathematical
libraries such as Flyspeck.Comment: journal version of arXiv:1310.2797 (which was submitted to LPAR
conference
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