# Joe

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I'm curious to all things new to me.

 13h comment Graph theory: Why people use “K” to represent complete graph?Thanks! Kazimierz Kuratowski was born in 1896. I cannot believe this fundamental concept was defined later than 1896. 13h comment Graph theory: Why people use “K” to represent complete graph?@Martin That's an possible explanation. In my opinion, they are fundamental concepts in graph theory hence it is not that easy to tell which one comes first. 13h comment Graph theory: Why people use “K” to represent complete graph?@martini I know nothing about German and google translation tells me that which possibly be wrong. 13h asked Graph theory: Why people use “K” to represent complete graph? Jan10 asked What's the relationship between interior/exterior/boundary point and limit point? Jan10 comment Real Analysis: Is $\emptyset$ a open set in $X$?If G is empty you can not choose a x that satisfies this. So G is not open. Jan10 asked Real Analysis: Is $\emptyset$ a open set in $X$? Jan9 revised What is the difference between open ball and neighborhood in real analysis?added 365 characters in body Jan9 asked What is the difference between open ball and neighborhood in real analysis? Dec31 accepted How to geometrically interpret $\sum^{p}_{1}\lambda_{i}(A)=\operatorname{tr}(A)$? Dec23 revised How to geometrically interpret $\sum^{p}_{1}\lambda_{i}(A)=\operatorname{tr}(A)$?added 170 characters in body Dec22 revised How to geometrically interpret $\sum^{p}_{1}\lambda_{i}(A)=\operatorname{tr}(A)$?added 121 characters in body Dec22 asked How to geometrically interpret $\sum^{p}_{1}\lambda_{i}(A)=\operatorname{tr}(A)$? Dec9 awarded Enthusiast Dec6 accepted How to understand spectral decomposition geometrically Nov29 asked How to understand spectral decomposition geometrically Nov27 accepted How to prove in a graph $G$, its incidence matrix $A$ is totally unimodular if and only if $G$ is a bipartite graph? Nov27 accepted Why $\sigma_{\bar{x}}=\frac{\sigma}{\sqrt{n}}$ Nov27 accepted What is degree of freedom in statistics? Nov27 accepted What's the relationship between Cauchy-Schwarz Inequality and Extended Cauchy-Schwarz Inequality?