Bicausal isomorphism of Bernoulli processes

Using an idea of Adler and Weiss, automorphisms of Bernoulli processes are constructed where the mapping in one direction is causal with bounded memory and the inverse mapping is causal with memory which is finite w.p.l. Nontrivial such automorphisms exist only when the letter probability distribution has nontrivial symmetry, e.g., the 2-shift.     

The even isomorphism theorem for Coxeter groups

Coxeter groups have presentations where for all , , and if and only if . A fundamental question in the theory of Coxeter groups is: Given two such ``Coxeter" presentations, do they present the same group? There are two known ways to change a Coxeter presentation, generally referred to as twisting and simplex exchange. We solve the isomorphism question for Coxeter groups with an even Coxeter presentation (one in which is even or when ). More specifically, we give an algorithm that describes a sequence of twists and triangle-edge exchanges that either converts an arbitrary finitely generated Coxeter presentation into a unique even presentation or identifies the group as a non-even Coxeter group. Our technique can be used to produce all Coxeter presentations for a given even Coxeter group.

     

Lusztig's isomorphism theorem for cellular algebras

In this paper, we first introduce a notion of semisimple system with parameters, then we establish Lusztig's isomorphism theorem for any cellular semisimple system with parameters. As an application, we obtain Lusztig's isomorphism theorem for Ariki-Koike algebras, cyclotomic q-Schur algebras and Birman-Murakami-Wenzl algebras. Second, using the results for certain Ariki-Koike algebras, we prove an analogue of Lusztig's isomorphism theorem for the cyclotomic Hecke algebras of type G(p,p,n) (which are not known to be cellular in general). These generalize earlier results of [G. Lusztig, On a theorem of Benson and Curtis, J. Algebra 71 (1981) 490-498.] on such isomorphisms for Iwahori-Hecke algebras associated to finite Weyl groups.     

An isomorphism extension theorem for Landau-Ginzburg B-models

Landau-Ginzburg mirror symmetry studies isomorphisms between A- and B-models, which are graded Frobenius algebras that are constructed using a weighted homogeneous polynomial W and a related symmetry group G. Given two polynomials W₁, W₂ with the same weights and same group G, the corresponding A-models built with (W₁,G) and (W₂,G) are isomorphic. Though the same result cannot hold in full generality for B-models, which correspond to orbifolded Milnor rings, we provide a partial analogue. In particular, we exhibit conditions where isomorphisms between unorbifolded B-models (or Milnor rings) can extend to isomorphisms between their corresponding orbifolded B-models (or orbifolded Milnor rings).     

The isomorphism theorem for relatively finitely determined Z n -actions

Any two ergodic Z ⁿ -actions which are finitely determined relative to a common factor are isomorphic if and only if they have the same entropy. This work supported in part by N.S.F. Grant DMS-85-04701.     

An isomorphism theorem for Teichmüller curves

It is proved that for any Fuchsian group Γ such that ℍ/Γ is a hyperbolic Riemann surface, the Teichmüller curve V(Γ) has a unique complex manifold structure so that the natural projection of the Bers fiber space F(Γ) onto V(Γ) is holomorphic with local holomorphic sections. An isomorphism theorem for Teichmüller curves is deduced, which generalizes a classical result that the Teichmüller curve V(Γ) depends only on the type of Γ and not on the orders of the elliptic elements of Γ when ℍ/Γ is a compact hyperbolic Riemann surface.     

On Bayes' theorem and the inverse Bernoulli theorem

A recent assertion by S. M. Stigler that Thomas Bayes was perhaps anticipated in the discovery of the result that today bears his name is exposed to further scrutiny here. The distinction between Bayes' theorem and the inverse Bernoulli theorem is examined, and pertinent early writings on this matter are discussed. A careful examination of the difference between these two theorems leads to the conclusion that a result given by David Hartley in 1749 is more in line with the inverse Bernoulli theorem than with Bayes' result, and it is suggested that there is not sufficient evidence to remove Bayes from his place as originator of the method adopted.     

Finitary isomorphism of some renewal processes to Bernoulli schemes

Using the marker and filler methods of Keane and Smorodinsky, we prove that entropy is a complete finitary isomorphism invariant for r-processes. It is conjectured that entropy is a complete finitary isomorphism invariant for finitary factors of Bernoulli schemes. We present a weaker version of this conjecture with hope that its proof is more attainable with present methods. In doing so, we define a one-way finitary isomorphism and prove one-way finitary results for random walks. We will also extend the marker and filler methods of Keane and Smorodinsky to a class of countable state processes.