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9h
comment Image of a normal space under a closed and continuous map is normal
why can we take neighbourhoods $V_1$ and $V_2$ contained in $f(U_1)$ and $f(U_2)$?
9h
accepted A countable Tychonoff space is normal?
9h
comment A countable Tychonoff space is normal?
oh ok, thank you kindly
9h
comment A countable Tychonoff space is normal?
Thank you, how do you prove this?
10h
asked A countable Tychonoff space is normal?
1d
answered How can I prove the Carmichael theorem
1d
comment Is the group $(\Bbb Z,+)$ isomorphic to the the group $(\Bbb Q\setminus\{0\},\cdot)$?
Yes I do, thank you.
1d
answered Is the group $(\Bbb Z,+)$ isomorphic to the the group $(\Bbb Q\setminus\{0\},\cdot)$?
1d
comment Elementary question in Group Theory with less prerequisite
@IttayWeiss thanks, you are right.
1d
answered Elementary question in Group Theory with less prerequisite
May
20
asked Product of two sets with density zero has density zero?
May
18
comment Prove or disprove: If $a^2 \mid bc$, then $a \mid b$ or $a \mid c$
Sure, happy to help.
May
18
answered Prove or disprove: If $a^2 \mid bc$, then $a \mid b$ or $a \mid c$
May
18
comment Endomorphic Function Definition
No, I'm a college student. There are some category theorists on this website, hopefully they can verify this. But I am almost 100% certain in this case.
May
18
comment Endomorphic Function Definition
Ok, I saw the link. It makes no sense at all. They never say what a surjective morphism is and in general this has no reason to be meaningful in any category. Of course in most examples of categories the morphisms are functions and so of course when talking about functions there is a notion of surjectivity. I am fairly certain that is a mistake.
May
18
comment Endomorphic Function Definition
Where did you read that, do you have a link?
May
18
comment Endomorphic Function Definition
No, an endomorphism is not a surjective morphism on an object to itself. Surjectivity is a property functions have. morphisms are not necessarily functions. The idea I am trying to give you is that categorically speaking we should not care about any properties a morphism has except for its domain, codomain and how it is composed with other morphisms.
May
18
answered Endomorphic Function Definition
May
18
answered What does “maximum order elements to mod n” mean for a number n without primitive roots modulo n?
May
18
comment What does “up to a subsequence” mean?
Sorry, perhaps I was not clear. Could you provide the source where you first read the phrase that made you want to know what it meant?