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Weierstrass and Blancmange nowhere differentiable functions,
Lebesgue integrable functions with everywhere divergent Fourier
series, and various nonintegrable Lebesgue measurable functions.
While dubbed strange or "pathological," these functions are
ubiquitous throughout mathematics and play an important role in
analysis, not only as counterexamples of seemingly true and natural
statements, but also to stimulate and inspire the further
development of real analysis. Strange Functions in Real Analysis
explores a number of important examples and constructions of
pathological functions. After introducing the basic concepts, the
author begins with Cantor and Peano-type functions, then moves to
functions whose constructions require essentially noneffective
methods. These include functions without the Baire property,
functions associated with a Hamel basis of the real line, and
Sierpinski-Zygmund functions that are discontinuous on each subset
of the real line having the cardinality continuum. Finally, he
considers examples of functions whose existence cannot be
established without the help of additional set-theoretical axioms
and demonstrates that their existence follows from certain
set-theoretical hypotheses, such as the Continuum Hypothesis.
The book is devoted to various constructions of sets which are
nonmeasurable with respect to invariant (more generally,
quasi-invariant) measures. Our starting point is the classical
Vitali theorem stating the existence of subsets of the real line
which are not measurable in the Lebesgue sense. This theorem
stimulated the development of the following interesting topics in
mathematics:
1. Paradoxical decompositions of sets in finite-dimensional
Euclidean spaces;
2. The theory of non-real-valued-measurable cardinals;
3. The theory of invariant (quasi-invariant)
extensions of invariant (quasi-invariant) measures.
These topics are under consideration in the book. The role of
nonmeasurable sets (functions) in point set theory and real
analysis is underlined and various classes of such sets (functions)
are investigated . Among them there are: Vitali sets, Bernstein
sets, Sierpinski sets, nontrivial solutions of the Cauchy
functional equation, absolutely nonmeasurable sets in uncountable
groups, absolutely nonmeasurable additive functions, thick uniform
subsets of the plane, small nonmeasurable sets, absolutely
negligible sets, etc. The importance of properties of nonmeasurable
sets for various aspects of the measure extension problem is shown.
It is also demonstrated that there are close relationships between
the existence of nonmeasurable sets and some deep questions of
axiomatic set theory, infinite combinatorics, set-theoretical
topology, general theory of commutative groups. Many open
attractive problems are formulated concerning nonmeasurable sets
and functions.
. highlights the importance of nonmeasurable sets (functions) for
general measure extension problem.
. Deep connections of the topic with set theory, real analysis,
infinite combinatorics, group theory and geometry of Euclidean
spaces shown and underlined.
. self-contained and accessible for a wide audience of potential
readers.
. Each chapter ends with exercises which provide valuable
additional information about nonmeasurable sets and
functions.
. Numerous open problems and questions."
This monograph gives the reader an up-to-date account of the fine
properties of real-valued functions and measures. The unifying
theme of the book is the notion of nonmeasurability, from which one
gets a full understanding of the structure of the subsets of the
real line and the maps between them. The material covered in this
book will be of interest to a wide audience of mathematicians,
particularly to those working in the realm of real analysis,
general topology, and probability theory. Set theorists interested
in the foundations of real analysis will find a detailed discussion
about the relationship between certain properties of the real
numbers and the ZFC axioms, Martin's axiom, and the continuum
hypothesis.
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