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Two examples concerning almost continuous functions

✍ Scribed by Krzysztof Ciesielski; Andrzej Rosl̵anowski


Publisher
Elsevier Science
Year
2000
Tongue
English
Weight
171 KB
Volume
103
Category
Article
ISSN
0166-8641

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✦ Synopsis


In this note we will construct, under the assumption that union of less than continuum many meager subsets of R is meager in R, an additive connectivity function f : R → R with Cantor intermediate value property which is not almost continuous. This gives a partial answer to a question of Banaszewski (1997). (See also Question 5.5 of Gibson and Natkaniec (1996-97).) We will also show that every extendable function g : R → R with a dense graph satisfies the following stronger version of the SCIVP property: for every a < b and every perfect set K between g(a) and g(b) there is a perfect set C ⊂ (a, b) such that g[C] ⊂ K and g C is continuous strictly increasing. This property is used to construct a ZFC example of an additive almost continuous function f : R → R which has the strong Cantor intermediate value property but is not extendable. This answers a question of Rosen (1997-98). This also generalizes Rosen's result (1997-98) that a similar (but not additive) function exists under the assumption of the Continuum Hypothesis, and gives a full answer to Question 3.11 of Gibson and Natkaniec (1996-1997).


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