completeness type properties and spaces of...
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COMPLETENESS TYPE PROPERTIES ANDSPACES OF CONTINUOUS FUNCTIONS
Ángel Tamariz-Mascarúa
Joint work with S. García-Ferreira and R. Rojas-Hernández
Universidad Nacional Autónoma de México
Workshop on Applied Topological StructuresUniversidad Politécnica de Valencia, June 22-23, 2016
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Initial conditions
In this talk space will mean Tychonoff space with more than onepoint.
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Introduction
Pseudocompact and Baire spaces are outstanding classesof spaces, but these properties are not productive.
Efforts have been made to define classes of spaces whichcontain all pseudocompact spaces, satisfy the BaireCategory Theorem and are closed under arbitrarytopological products.
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Figura: Productive Complete Properties
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Introduction
One of these properties is Oxtoby completeness.
Another is Todd completeness.
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Completeness type propertie
Definition 2.1.A family B of sets in a topological space X is called π-base
(respectively, π-pseudobase)
if every element of B is open
(respectively, has a nonempty interior)
and every nonempty open set in X contains an element of B.
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Figura: A π-base
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Completeness type properties
Definition 2.2.A space X is Oxtoby complete (respectively, Todd complete) ifthere is a sequence
{Bn : n < ω}
of π-bases, (respectively, π-pseudobases) in X such that forany sequence {Un : n < ω} where
Un ∈ Bn and clX Un+1 ⊆ intX Un for all n,
then ⋂n<ω
Un 6= ∅.
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Figura: An Oxtoby Sequence
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Completeness type properties
There are also, properties of type completeness defined bytopological games:
Definition 2.3A space Z is weakly α-favorable if Player II has a winningstrategy in the Banach-Mazur game BM(Z ).
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Figura: The Banach-Mazur game
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Completeness type properties
The relations between all these properties are:
Pseudocompact ⇒ Oxtoby complete ⇒ Todd complete
Todd complete ⇒ weakly α-favorable ⇒ Baire
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Spaces of continuous functions
We know:
Proposition 3.1
Cp(X ) is never pseudocompact.
Proposition 3.2, van Douwen, Pytkeev
Cp(X ) is a Baire space iff every pairwise disjoint sequence offinite subsets of X has a strongly discrete subsequence.
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Spaces of continuous functions
We want to say something about the completenesproperties just presented in spaces of the real-valuedcontinuous functions with the pointwise convergencetopology Cp(X ). Mainly, we want to relate these propertieswith properties defined in X . In order to do this we define:
Definition 3.3A space X is u-discrete if every countable subset of X isdiscrete and C-embedded in X .
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Spaces of continuous functions
D.J. Lutzer and R.A. McCoy analyzed Oxtobypseudocompleteness in Cp(X ). They proved:
Theorem 3.2, 1980Let X be a pseudonormal space. Then the following areequivalent:1.- X is u-discrete.
2.- Cp(X ) is Oxtoby complete.
3.- Cp(X ) is weakly α-favorable.
4.- Cp(X ) is Gδ-dense in RX .
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Spaces of continuous functions
Afterwards, A. Dorantes-Aldama, R. Rojas-Hernández and Á.Tamariz-Mascarúa improve the Lutzer and McCoy result:
Theorem 3.3, 2015Let X be a space with property D of van Douwen. Then thefollowing are equivalent:
1.-X is u-discrete.
2.- Cp(X ) is Todd complete.
3.- Cp(X ) is Oxtoby complete.
4.- Cp(X ) is weakly α-favorable.
5.- Cp(X ) is Gδ-dense in RX .
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Spaces of continuous functions
And A. Dorantes-Aldama and D. Shakhmatov proved:
Theorem 3.4, 2016The following staments are equivalent:
1.- X is u-discrete.
2.- Cp(X ) is Todd complete.
3.- Cp(X ) is Oxtoby complete.
4.- Cp(X ) is Gδ-dense in RX .
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Spaces of continuous functions
Finally, S. García-Ferreira, R. Rojas-Hernández and Á.Tamariz-Mascarúa proved:
Theorem 3.5, 2016Cp(X ) is weakly α-favorable if and only if X is u-discrete.
And so,
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Theorem 3.6, 2016The following conditions are equivalent.
1.- X is u-discrete;
2.- Cp(X ) is Todd complete;
3.- Cp(X ) is Oxtoby complete;
4.- Cp(X ) is weakly α-favorable;
5.- Cp(X ) is Gδ-dense in RX .
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Weakly pseudocompact spaces
Theorem 4.1. (Hewitt, 1948)A space X is pseudocompact if and only if it is Gδ-dense in βX(iff it is Gδ-dense in any of its compactifications).
So, a natural generalization of pseudocompactness is:
Definition 4.2. (García-Ferreira and García-Máynez, 1994)A space is weakly pseudocompact if it is Gδ-dense in some ofits compactifications.
Then every pseudocompact space is weaklypseudocompact.
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Weakly pseudocompact spaces
Theorem 4.3. (García-Ferreira and García-Máynez, 1994)
Every weakly pseudocompact space is Baire.
Weak pseudocompactness is productive.
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Weakly pseudocompact spaces
Example of weakly pseudocompact spaces:
1.- The non-countable discrete spaces.
2.- (F.W. Eckertson, 1996)The metrizable hedgehog J(κ) with κ > ω.
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We can add “Cp(X ) is weakly pseudocompact"to the list ofthe following theorem?
Theorem 3.6, 2016The following conditions are equivalent.1.- X is u-discrete;
2.- Cp(X ) is Todd complete;
3.- Cp(X ) is Oxtoby complete;
4.- Cp(X ) is weakly α-favorable;
5.- Cp(X ) is Gδ-dense in RX .
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Weakly pseudocompact spaces
With respect to this problem we have:
Theorem 4.3, S. García-Ferreira, R. Rojas-Hernández, Á.Tamariz-Mascarúa, 2016If Rκ is weakly pseudocompact for some cardinal κ, then Rc isweakly pseudocompact.
Theorem 4.4The space Rκ is weakly pseudocompact if and only if Cp(X ) isweakly pseudocompact for every u-discrete space X withmin{c, κ} ≤ |X |.
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Theorem 3.6, 2016If Rω1 is weakly pseudocompact, then the following conditionsare equivalent.
1.- X is u-discrete;
2.- Cp(X ) is weakly pseudocompact;
3.- Cp(X ) is Todd complete;
4.- Cp(X ) is Oxtoby complete;
5.- Cp(X ) is weakly α-favorable;
6.- Cp(X ) is Gδ-dense in RX .
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS
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Weakly pseudocompact spaces
Problem 6.1Is Rω1 weakly pseudocompact?
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Topological groups
One interesting consequence of the results mentioned in thistalk that we got are generalizations of the classic Tkachuk’sTheorem:
Theorem 5.1, V. Tkachuk, 1987Cp(X ) ∼= Rκ if and only if X is discrete of cardinality κ.
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Topological groups
We obtained:
Theorem 5.2Let G be a separable completely metrizable topological groupand X a set. If H is a dense subgroup of GX and H ishomeomorphic to GY for some set Y , then H = GX .
Corollary 5.3Let X be a space and let G be a separable completelymetrizable topological group. If Cp(X , G) is homeomorphic toGY for some set Y , then Cp(X , G) = GX .
Joint work with S. García-Ferreira and R. Rojas-HernándezCOMPLETENESS TYPE PROPERTIES AND SPACES OF CONTINUOUS FUNCTIONS