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11h
accepted Ordinal enumeration in ordered Mostowski model - does it not need the global choice?
13h
asked Ordinal enumeration in ordered Mostowski model - does it not need the global choice?
Feb
6
answered find $\lim_{n\to\infty}(1+\frac{1}{3})(1+\frac{1}{3^2})(1+\frac{1}{3^4})\cdots(1+\frac{1}{3^{2^n}})$
Feb
6
answered Does ZFC allow for the existence of any paradoxical sets?
Feb
1
revised Definition of “well defined” in mathematics
edited tags
Jan
31
accepted Well-foundedness of cardinals and the axiom of choice
Jan
31
revised How to simulate power sets in structural set theory (ETCS)?
edited tags
Jan
31
revised Prove that $a^2+b^2+16\ge ab+4a+4b$ for all $a, b$.
edited title
Jan
31
asked Well-foundedness of cardinals and the axiom of choice
Jan
30
accepted Is there a domain which is not UFD but has a maximal principal ideal?
Jan
29
comment Is there a domain which is not UFD but has a maximal principal ideal?
@Mathmo123 Oh, I don't think $(\sqrt{-5})$ (I only consider the principal ideal generated by 2.) I realize that the answer sometimes hidden in obvious thing, again. Thanks
Jan
29
revised Is there a domain which is not UFD but has a maximal principal ideal?
added 58 characters in body; edited title
Jan
29
comment Is there a domain which is not UFD but has a maximal principal ideal?
@rschwieb Yes, I confuse a ring and a domain because I have not learn about non-domain ring deeply. I am going to modify them.
Jan
29
asked Is there a domain which is not UFD but has a maximal principal ideal?
Jan
27
revised What is Representation Theory?
edited tags
Jan
27
revised Determining the kernel of a function and finding the direct image of a set
added 42 characters in body
Jan
27
comment Determining the kernel of a function and finding the direct image of a set
Is it have the kernel? The function looks like not algebraic so we can not talk about the kernel of the function.
Jan
25
revised Show that $F\subset Y$ is closed in $Y$ iff $F=Y\;\cap\;H$ where $H\subset X$ is closed in $X$.
edited tags
Jan
24
comment How to picture a first countable space?
First-countability can be stated as: "the space has countable local basis". It may not give any intuition but provides good clues to remember.
Jan
22
revised Finding cardinality of a set which sum of its elements equal to an integer
edited tags