Talk:Proper forcing axiom
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[edit] Notation question
[λ]ω Am I correct that this is the power set of λ restricted to subsets that are countable (of size ω).? Thanks! Zero sharp 05:27, 25 October 2007 (UTC)
- Basically. Sometimes it's taken to mean the set of all strictly increasing functions from ω to λ, but it comes to the same thing. I'm a little surprised to see the notation in this context; I would have expected more
, which means exactly "countable (including finite) subsets of λ". --Trovatore 23:51, 25 October 2007 (UTC)
- Whoops, my bad; it doesn't come to the same thing. Of course not every countable subset of λ is the range of an increasing function from ω. I think this should be examined to see which version is actually meant here. I sort of suspect the version with is more standard. --Trovatore 23:58, 25 October 2007 (UTC)
- Whoops, my bad; it doesn't come to the same thing. Of course not every countable subset of λ is the range of an increasing function from ω. I think this should be examined to see which version is actually meant here. I sort of suspect the version with
