# Ostap Chervak

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## Registered User

 Name Ostap Chervak Member for 2 years Seen May 18 at 13:22 Website Location Lviv Age 20
Interests: Ramsey theory, General Topology, Asymptotic Topology, Dimension Theory, Algebraic Topology, Commutative rings, Set Theory, Forcing, General Number Theory
 May9 comment Bijection from $\mathbb{R}$ to $\mathbb{R^2}$How can you do the second step? I don't see an imediate way of building a bijection between $\mathbb{R}$ and $\mathbb{R}\setminus\mathbb{Q}$ May4 comment Awfully sophisticated proof for simple factsThis prove shows that there exist a field with 83 elements Jan31 comment Colloquial catchy statements encoding serious mathematicsA city is compact if you can fire all except finite number of policemen patrolling the city Jan23 comment nontrivial theorems with trivial proofsNote that this indeed is a generalization: original Euclid's proof uses $I=\emptyset$ Jan19 comment Magic trick based on deep mathematicsAny hints on solving this problem? Jan19 comment What is the field with one element?"F_un mathematics" spin off exists, it's just isn't a website Jan17 comment What are the most misleading alternate definitions in taught mathematics?And how to define paracompactness then? If you define it in terms of decompositions of unit you lose conection with compactness Jan16 revised Estimate on radical of $2^n \pm 1$deleted 143 characters in body Jan15 comment Estimate on radical of $2^n \pm 1$$2^n + 1 = (2^n + 1) \rightarrow 2^n+1 \leq rad (1\times 2\times (2^n+1))^2 \rightarrow 2rad(2^n+1) \geq \sqrt{2^n+1}$ Thank you, quid, sorry for that Jan15 comment Is there a (standard) name for $\bar{A}\setminus A$?If space is compact you may use the word "remainder" Jan15 revised Estimate on radical of $2^n \pm 1$deleted 2 characters in body Jan15 revised Estimate on radical of $2^n \pm 1$added 165 characters in body; deleted 2 characters in body; added 6 characters in body Jan15 asked Estimate on radical of $2^n \pm 1$ Jan12 comment Mochizuki’s proof and Siegel zerossomething may be clear while not being clearly clear Jan4 comment Awfully sophisticated proof for simple factsIrrartionality of $\pi$ uses infinitude of primes, so proofs by zeta function are all circular – Jan2 awarded ● Popular Question Dec31 answered Old books still used Dec5 comment A profinite group which is not its own profinite completion?In fact $G/H$ is an ultrapower of $T$ but ultrapower of finite set is isomorphic to it. Dec4 comment Why is there no Borel function mapping every countable set of reals outside itself?Existence of non-measurables is equivalent to $\aleph_1 \leq |\mathbb {R}|$