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location Brazil
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22h
comment Are Borel sets preserved by an open continuous map?
Does this question have any motivation and/or you have any idea on how to solve this?
22h
comment Let $P, Q, R$ be finite posets. Prove that $P^{Q+R} \cong P^Q \times P^R$.
This seems good enough for me. Note that you didn't use finiteness nor that $P$ and $Q$ are posets.
1d
revised If $p(z)$ is an injective polynomial $\Longrightarrow$ $p(z)=az+b$
added 211 characters in body
1d
revised If $p(z)$ is an injective polynomial $\Longrightarrow$ $p(z)=az+b$
added 211 characters in body
1d
answered If $p(z)$ is an injective polynomial $\Longrightarrow$ $p(z)=az+b$
2d
comment Explain rings and is [S, /, -] a ring?
@Colin I added a little explanation about functions and cartesian products. Hope it helps a little. Also, binary functions or operations are the same thing, it's just a matter of preference (the same way that functions are also called operators, maps, etc...).
2d
revised Explain rings and is [S, /, -] a ring?
further explanations
2d
comment Explain rings and is [S, /, -] a ring?
Yes. The result of operations are in the codomain, which is the (underlying set of) the ring/group.
2d
revised Explain rings and is [S, /, -] a ring?
added 424 characters in body
2d
answered Explain rings and is [S, /, -] a ring?
2d
revised how to show a function is bijection
added 936 characters in body
2d
answered how to show a function is bijection
Aug
26
answered A question about a proof of the “Least Upper Bound Property” in the Tao's Real Analysis notes
Aug
26
revised A question about a proof of the “Least Upper Bound Property” in the Tao's Real Analysis notes
latexified it
Aug
25
revised How prove can't exist a set $A$ of positive integers satisfying the two conditions
Lots of formatting
Aug
25
reviewed Approve suggested edit on If $\sin( 2 \theta) = \cos( 3)$ and $\theta \leq 90°$, find $\theta$
Aug
23
awarded  Nice Answer
Aug
22
comment $Ker(T) \subseteq V$ Is A Subspace
You have to prove that $\ker(T)$. Satisfies the axioms for subspaces: if $x$ and $y\in\ker(T)$, show that $x+y\in\ker(T)$, and that if $x\in\ker(T)$ and $\lambda$ is a scalar, then $\lambda x\in\ker(T)$.
Aug
21
comment Subgroup Decision Problem
Are $p$ and $q$ different? Dos $G_p$ have order $p$ and $G_q$ has order $q$?
Aug
20
comment Can the winding number be infinite?
I believe that the curve must be rectifiable (i.e. have finite length) by hipothesis. At least Wikipedia makes this hipothesis when defining line integral (in particular winding number).