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asked Does there exist a quadratic generalization of the continued fraction approximants?
Mar
10
comment Jech's Set Theory logic prerequisites
@Nectric: I'd say Jech's book is actually fairly self-contained; but its scope is far too large for it to be anything other than a reference. Plus, its treatment of certain topics (forcing in particular) is not what I would want for a beginner.
Mar
10
answered Jech's Set Theory logic prerequisites
Mar
6
answered Existence of an uncountable set of sequence
Feb
24
revised Initial segments of trees
Not all subsets are initial segments.
Feb
21
awarded  Enthusiast
Feb
18
comment Questions of $\mathbb{P}$-name for a set and functions
Which $p$ are you talking about in your two questions?
Feb
17
answered Initial segments of trees
Feb
13
comment Question of $\Diamond$ in Generic Extension
Apply $\diamondsuit$ to the $\mathbb{P}$-names for subsets of $\omega_1$? (By the ccc, you can code such a name as an $\omega_1$-sequence of countable subsets of $\mathbb{P}$.)
Jan
28
comment Measurability Question?
@anthonyquas: isn't it pretty direct from the definitions? A reverse well ordering is a linear order with no infinite, strictly increasing subset.
Jan
27
comment Measurability Question?
If $X$ is a Polish space and $\mathcal{B}$ is the $\sigma$-algebra of Borel sets, then $S$ looks like it's analytic and hence measurable with respect to any complete Borel measure. I'm not sure that it's not Borel, though.
Jan
21
comment Is there a bijective mapping $f:\mathbb{N}^2→\mathbb{N}$ that preserves lexicographic order?
Yup! And these are some more characters.
Jan
21
comment Is there a bijective mapping $f:\mathbb{N}^2→\mathbb{N}$ that preserves lexicographic order?
It doesn't matter. Let $a_n = f(0,n)$. Then you can say certain things about the $a_n$'s; namely, they're increasing. So where is $f(1,0)$ relative to the $a_n$'s?
Jan
21
comment Is there a bijective mapping $f:\mathbb{N}^2→\mathbb{N}$ that preserves lexicographic order?
Look at where the pairs $(0,n)$ are sent. Now where is the image of $(1,0)$ relative to them?
Jan
15
answered When should I be doing cohomology?
Jan
6
revised A question about $\aleph_1$-dense sets and the basis problem for uncountable linear orderings
added 69 characters in body
Jan
6
answered A question about $\aleph_1$-dense sets and the basis problem for uncountable linear orderings
Dec
22
awarded  Yearling
Dec
22
comment Prove $ℝ^I$ is not Lindelöf
Have you tried looking at any natural open covers?
Dec
10
accepted Separating disjoint sets of size $\aleph_1$ with Borel sets