How to show this countable problem
22240
Every infinite subset of a countable set is countable.
157513
How can I prove that these sets are countable infinite?
93886
how can I show this question : function
118595
Proving that a set is countable by finding a bijection
132778
All distances are rational prove the set is countable
152563
Set of discontinuity of monotone function is countable
154474
Image of countable and uncountable sets
146055
Proving a set of functions is uncountable
102543
Real definition of "countable set"
127356
Using Count to find the number of occurrences
155777
Show that infinite Cartesian product is uncountable
72750
Uncountable number of mutually disjoint countable sets in $\mathbb R$
14409
A problem about function N
27802
How to show this equals 1 without "calculations"
127100
Countable or uncountable set 8 signs
94438
Show that the countable product of metric spaces is metrizable
141496
Could someone make the proof into a hinted exercise?