Exercise 1.4.8. The following construction generalizes the construction of the reals from the rationals in Chapter 5, allowing one to view any metric space as a subspace of a complete metric space. In what follows we let (X,d) be a metric space. n→ ∞ Yn (a) Given any Cauchy sequence (xn)x1 in X, we introduce the formal limit LIMn on. We say that two formal limits LIM∞ xn and LIMn- are equal if lim→∞ d(xn, Yn) is equal to zero. Show that this equality relation obeys the reflexive, symmetry, and transitive axioms. (b) Let X be the space of all formal limits of Cauchy sequences in X, with the above equality relation. Define a metric dx: XxX → R+ by setting dx (LIMn→∞ xn, LIM→∞ Yn) := lim_d(xn, Yn). n→X Show that this function is well-defined (this means not only that the limit lim→∞ d(xn, Yn) exists, but also that the axiom of substitution is obeyed; cf. Lemma 5.3.7), and gives X the structure of a metric space. (c) Show that the metric space (X, dx) is complete.

Linear Algebra: A Modern Introduction
4th Edition
ISBN:9781285463247
Author:David Poole
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Chapter1: Vectors
Section1.1: The Geometry And Algebra Of Vectors
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Exercise 1.4.8. The following construction generalizes the construction of the
reals from the rationals in Chapter 5, allowing one to view any metric space
as a subspace of a complete metric space. In what follows we let (X,d) be a
metric space.
n→ ∞ Yn
(a) Given any Cauchy sequence (xn)x1 in X, we introduce the formal limit
LIMn on. We say that two formal limits LIM∞ xn and LIMn-
are equal if lim→∞ d(xn, Yn) is equal to zero. Show that this equality
relation obeys the reflexive, symmetry, and transitive axioms.
(b) Let X be the space of all formal limits of Cauchy sequences in X, with
the above equality relation. Define a metric dx: XxX → R+ by setting
dx (LIMn→∞ xn, LIM→∞ Yn) := lim_d(xn, Yn).
n→X
Show that this function is well-defined (this means not only that the
limit lim→∞ d(xn, Yn) exists, but also that the axiom of substitution is
obeyed; cf. Lemma 5.3.7), and gives X the structure of a metric space.
(c) Show that the metric space (X, dx) is complete.
Transcribed Image Text:Exercise 1.4.8. The following construction generalizes the construction of the reals from the rationals in Chapter 5, allowing one to view any metric space as a subspace of a complete metric space. In what follows we let (X,d) be a metric space. n→ ∞ Yn (a) Given any Cauchy sequence (xn)x1 in X, we introduce the formal limit LIMn on. We say that two formal limits LIM∞ xn and LIMn- are equal if lim→∞ d(xn, Yn) is equal to zero. Show that this equality relation obeys the reflexive, symmetry, and transitive axioms. (b) Let X be the space of all formal limits of Cauchy sequences in X, with the above equality relation. Define a metric dx: XxX → R+ by setting dx (LIMn→∞ xn, LIM→∞ Yn) := lim_d(xn, Yn). n→X Show that this function is well-defined (this means not only that the limit lim→∞ d(xn, Yn) exists, but also that the axiom of substitution is obeyed; cf. Lemma 5.3.7), and gives X the structure of a metric space. (c) Show that the metric space (X, dx) is complete.
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