Ittay Weiss
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 12h revised Metric assuming the value infinity deleted 1 character in body 16h awarded Good Answer Apr 24 comment What is the maximum value of $\int_{0}^{2}{h(t)}dt$? welcome to MSE. Please note this is not a good way to pose a question here. What is the purpose of you asking this question here? What have you tried? Where are you stuck? You have to be clear about these things if you want to get helpful answers. Apr 21 accepted compact-open metrizability Apr 17 comment Limit point symmetric? Assuming your interpretation of $x$ is a limit point of $y$ is that $x$ belongs to the closure of $\{y\}$, the answer is that in an arbitrary topological space $X$ the relation $x\in Cl(y)$ need not imply $y\in Cl(x)$, as is very well-known. Very minimal separation conditions do imply the implication, as is also very well-known. Apr 16 comment Is set membership relation a set? If the set of all sets exists (call it $U$), then the membership relation is the set $\{(x,y)\in U\times U\mid x\in y\}$. So if the set theory you work with allows for the constructions needed for this definition of a set, then you're done. Apr 14 comment Why isn't '&' used for logical conjunction? @Constantine just like painting is not about brushes, but a question about a new style of brush certainly is of interest and belongs to world of painting, so is mathematics not about notation, but a question about some notational style is of interest and belongs to the world of mathematics. Apr 14 comment Why isn't '&' used for logical conjunction? you may wish to correct the year for Peano. I doubt he practiced mathematics in 1988.... Apr 13 awarded Necromancer Apr 12 comment closed union of closed sets Would anything go wrong if one takes the upper Vietoris topology? or the Vietoris topology? Apr 12 comment Proof that $0^0 \neq 1$ what is your definition of $0^0$? Apr 12 comment closed union of closed sets I'm interested in a convenient formalism for upper/lower semicontinuous functions, primarily in the context of generalised inverse limits of compacta (and generalisations thereof). Apr 12 comment closed union of closed sets Yes @StuKraji do you have a good reference? Apr 11 awarded Nice Question Apr 11 awarded Nice Answer Apr 8 comment why can't quintics be solved by radicals and the relevance of permutations of roots of polynomials perhaps you would like to read Galois' original text as well.... Joking aside, the modern treatment through Galois theory is an enormous simplification over any of the original treatments. Tackling, say, Abel's work directly is going to be extremely challenging, while there are several excellent books that go from nothing to the Galois correspondence in under 150 pages, complete with all the linear algebra and group theory prerequisites, and applications not only to the insolubility of the quintic, but (why not, it's so easy once you have Galois) other famous results. Apr 6 revised Prove that $A^k = 0$ iff $A^2 = 0$ added 4 characters in body Apr 3 comment How many quadratic extension are there on a field? Do you think that $\mathbb Q (\sqrt 2)$ is isomorphic to $\mathbb Q (\sqrt 3)$? Try to construct an isomorphism. Apr 3 answered limit functors as adjoints Mar 29 comment Why is cardinality of set of even numbers = set of whole numbers? @nxs responding to your comment to me, you seem to confuse abstract with arbitrary. There is nothing arbitrary in the choice of axioms for the things we study, no matter how abstract or concrete they are.