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Equality sets for recursively enumerable languages

Vesa Halava, Tero Harju, Hendrik Jan Hoogeboom, Michel Latteux (2005)

RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications

We consider shifted equality sets of the form E G ( a , g 1 , g 2 ) = { w ∣ g 1 ( w ) = a g 2 ( w ) } , where g 1 and g 2 are nonerasing morphisms and a is a letter. We are interested in the family consisting of the languages h ( E G ( J ) ) , where h is a coding and E G ( J ) is a shifted equality set. We prove several closure properties for this family. Moreover, we show that every recursively enumerable language L ⊆ A * is a projection of a shifted equality set, that is, L = π A ( E G ( a , g 1 , g 2 ) ) for some (nonerasing) morphisms g 1 and g 2 and a letter a , where π A deletes the letters not in A . Then we deduce...

Equality sets for recursively enumerable languages

Vesa Halava, Tero Harju, Hendrik Jan Hoogeboom, Michel Latteux (2010)

RAIRO - Theoretical Informatics and Applications

We consider shifted equality sets of the form EG(a,g1,g2) = {ω | g1(ω) = ag2(ω)}, where g1 and g2 are nonerasing morphisms and a is a letter. We are interested in the family consisting of the languages h(EG(J)), where h is a coding and (EG(J)) is a shifted equality set. We prove several closure properties for this family. Moreover, we show that every recursively enumerable language L ⊆ A* is a projection of a shifted equality set, that is, L = πA(EG(a,g1,g2)) for some (nonerasing) morphisms g1...

Equational spectrum of Hilbert varieties

R. Padmanabhan, Sergiu Rudeanu (2009)

Open Mathematics

We prove that an equational class of Hilbert algebras cannot be defined by a single equation. In particular Hilbert algebras and implication algebras are not one-based. Also, we use a seminal theorem of Alfred Tarski in equational logic to characterize the set of cardinalities of all finite irredundant bases of the varieties of Hilbert algebras, implication algebras and commutative BCK algebras: all these varieties can be defined by independent bases of n elements, for each n > 1.

Equimorphism invariants for scattered linear orderings

Antonio Montalbán (2006)

Fundamenta Mathematicae

Two linear orderings are equimorphic if they can be embedded in each other. We define invariants for scattered linear orderings which classify them up to equimorphism. Essentially, these invariants are finite sequences of finite trees with ordinal labels. Also, for each ordinal α, we explicitly describe the finite set of minimal scattered equimorphism types of Hausdorff rank α. We compute the invariants of each of these minimal types..

Equivalence relations induced by some locally compact groups of homeomorphisms of 2 ℕ

B. Majcher-Iwanow (2005)

Colloquium Mathematicae

Let T be a locally finite rooted tree and B(T) be the boundary space of T. We study locally compact subgroups of the group TH(B(T)) = ⟨Iso(T),V⟩ generated by the group Iso(T) of all isometries of B(T) and the group V of Richard Thompson. We describe orbit equivalence relations arising from actions of these groups on B(T).

Equivalent Expressions of Direct Sum Decomposition of Groups1

Kazuhisa Nakasho, Hiroyuki Okazaki, Hiroshi Yamazaki, Yasunari Shidama (2015)

Formalized Mathematics

In this article, the equivalent expressions of the direct sum decomposition of groups are mainly discussed. In the first section, we formalize the fact that the internal direct sum decomposition can be defined as normal subgroups and some of their properties. In the second section, we formalize an equivalent form of internal direct sum of commutative groups. In the last section, we formalize that the external direct sum leads an internal direct sum. We referred to [19], [18] [8] and [14] in the...

Equivalent fuzzy sets

Branimir Šešelja, Andreja Tepavčević (2005)

Kybernetika

Necessary and sufficient conditions under which two fuzzy sets (in the most general, poset valued setting) with the same domain have equal families of cut sets are given. The corresponding equivalence relation on the related fuzzy power set is investigated. Relationship of poset valued fuzzy sets and fuzzy sets for which the co-domain is Dedekind-MacNeille completion of that posets is deduced.

Equivariant measurable liftings

Nicolas Monod (2015)

Fundamenta Mathematicae

We discuss equivariance for linear liftings of measurable functions. Existence is established when a transformation group acts amenably, as e.g. the Möbius group of the projective line. Since the general proof is very simple but not explicit, we also provide a much more explicit lifting for semisimple Lie groups acting on their Furstenberg boundary, using unrestricted Fatou convergence. This setting is relevant to L ∞ -cocycles for characteristic classes.

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