176,575 reputation
17243487
bio website boolesrings.org/asafk
location Israel
age 29
visits member for 4 years, 4 months
seen 2 hours ago

Ph.D. student in the Hebrew University of Jerusalem.

Set theorist to-be.


5h
comment Mathematical Christmas Anecdotes, Stories and Problems
What about other seasonal holidays? Hanukkah, Kwanza, winter/summer solstice?
7h
revised Pebble Problem Maximum$=\big\lceil \log_3(n)\big\rceil$?
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18h
comment The cardinal of the set of all measures on $\mathbb{R}$
When you say that the measure is into $\Bbb R$, do you mean that it only gives finite values?
18h
comment The cardinal of the set of all measures on $\mathbb{R}$
Oh, that's a good point. Let's ask for clarification in the comments.
18h
revised The cardinal of the set of all measures on $\mathbb{R}$
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18h
answered The cardinal of the set of all measures on $\mathbb{R}$
20h
revised Is this a valid proof for $1+1=2$?
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20h
comment Is this a valid proof for $1+1=2$?
See also: this and that. And probably a few more.
20h
comment Is this a valid proof for $1+1=2$?
You haven't told us how you define $2$, or what are the available operations and relations in your language.
23h
awarded  definition
1d
comment Proving projection map is onto
The projection map is from a Cartesian product onto one of the coordinates. This is a quotient map, since we "divide" by the equivalence relation, and it is somewhat like a quotient. As for helping, you have an answer. I would have left a short hint: use reflexivity of the relation.
1d
comment Proving projection map is onto
I wouldn't call this the projection map. Maybe the quotient map.
1d
comment Inverse of a set, possible?
@user202593: I am almost ashamed at how little I knew about choice back then. In these three and a half years I have learned so much more, and developed my intuition so much. In part because I answered so many questions online, and learned a lot from writing them. In any case, see the link I posted under your answer for my take on negative cardinality.
1d
comment Inverse of a set, possible?
There is already an operation which returns the content of a singleton. $$\bigcup\{x\}=x$$
1d
comment Group of order 30 can't be simple
Nowadays being 30 is far from simple. It's something that is reflected in group theory.
1d
comment Inverse of a set, possible?
About negative cardinality.
1d
comment Is every countable ordinal homeomorphic to a subspace of $\mathbb R$?
I do, thanks for the correction!
1d
comment Could “$\infty$” be understood by taking the reciprocals of the Hyperreal numbers?
I find the term "transfinite number" better.
1d
comment Is every countable ordinal homeomorphic to a subspace of $\mathbb R$?
Yeah, that is essentially the plan.
1d
revised Is every countable ordinal homeomorphic to a subspace of $\mathbb R$?
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