# Jay Kangel

Age: 65

I have a BA in math from the University of Minnesota. I am interested in convexity.
 15h asked How do I log out from the new interface? 15h comment Concern about lesser attention towards relatively advanced questionsI once got a message that I was voting on answers but I should consider voting on more questions. (approximate wording) Perhaps there could be notices of people selecting favorite questions within our favorite tags. 1d comment Change in Rank of matrixPerhaps you could compute the rank of the matrix as a function of $g_1, \cdots, g_5$. 1d reviewed Reviewed Change in Rank of matrix 1d comment Change in Rank of matrixIf you show us what you have tried someone may be ab le to use your work to provide a hint or answer. 1d reviewed No Action Needed Proving a subset $A$ of a metric space $(X,d)$ is open Dec 3 reviewed Reviewed What multiplies to this and adds to that? Dec 3 reviewed Reviewed Closed sets, boundary, topology. Dec 3 comment Closed sets, boundary, topology.If you show us what you have tried perhaps someone can use your work as a basis for a hint or answer. Dec 3 comment Prove that $f(x)=x$ for all $x\geq 0$In the first sentence of your attempted proof you are assuming what you intend to prove. Dec 3 answered Examples of poor review audits Dec 2 reviewed No Action Needed Restriction on Graph Automorphism Dec 2 reviewed Reviewed Proof about Newton: Homework Dec 2 reviewed Reviewed Ordinary Differential Equations with initial conditions Dec 1 reviewed Reviewed Trigonometric Identities HW Dec 1 comment Are questions of all levels acceptable on this site?+1 for the last sentence. Nov 30 reviewed No Action Needed Compute $a(x)b(x)+c(x)$ in $\mathrm{GF}(2^4)$ where the irreducible generator polynomial $x^4+x+1$. Nov 30 comment Give an example of a nonempty finite set which is neither open nor closed?Sets like $\mathbb{R}$ and spaces like metric spaces have usual topologies. Please refer to tomasz's fine answer for this situation. Using the word informally, a "random" set does not have a usual topology. Nov 30 comment Give an example of a nonempty finite set which is neither open nor closed?@BillyThorton The trivial topology for a set $X$ is the smallest possible topology for the set. That is to say, only $\varnothing$ and $X$ are open. Nov 30 revised Give an example of a nonempty finite set which is neither open nor closed?Removed reference to trivial topology.