A set $\displaystyle X$ is said to be denumerable provided that $\displaystyle X\sim N.$
A countable set is a set which is either finite or denumerable.
(Lin p122 Definition 3)

http://www.gabormelli.com/RKB/Countable_Set

https://ko.wikipedia.org/wiki/가산_집합

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countable set

가산성,countability 집합,set
=,countability . countability {
가산성
가산성
}