http://i49.tinypic.com/v2tpjr.jpg

Did I prove this sufficiently?

- Feb 9th 2010, 01:44 PMdavismjProof that the intersection of infinitely many countable sets is countable.
http://i49.tinypic.com/v2tpjr.jpg

Did I prove this sufficiently? - Feb 9th 2010, 01:51 PMDrexel28
You mean union.

a) Proving by induction implies that the union of a fixed arbitrarily large number of countable sets is countable. It says nothing about letting range freely over the naturals.

b) The second part confuses me. The best way to do this is to first prove that if is surjective, then is countable and then note that where (where is the bijection from to ) is a surjection.