I came across a statement that "every countable set is the range of a 1-1 function defined on J" under Definition 2.7 on Page 26 of the book The principles of Mathematic Analysis. So must a countable set be infinite? If no, what does that statement mean? If yes, is a finite set a countable set? Thanks.
2026-03-30 13:52:12.1774878732
Must a countable set be infinite?
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