Chapter 1: E1.1 Solution
Working problems is a crucial part of learning mathematics. No one can learn topology merely by poring over the definitions, theorems, and examples that are worked out in the text. One must work part of it out for oneself. To provide that opportunity is the purpose of the exercises.
James R. Munkres
’Probability’ for subsets of
Let
. Say that
has (Cesàro) density
and write
if
exists. Give an example of sets
and
in
for which
. Thus,
is not an algebra.
If
is a subset of
such that for every pair of numbers
and
exactly one number is in
, then
with
. Let
be the set of odd numbers. Let
be the set that includes
, and all even numbers
, and all odd numbers
. So,
Then, the intersection
includes
and all odd numbers
. Let
Then,
In particular,
Therefore, the limit
does not exist.