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 Mar30 accepted The number of $n$-tuples with a sum less than $m$ is $C_m^n$? Dec10 accepted You only need countable many sets each time in a generated $\sigma$-algebra, right? Nov5 accepted How do I prove that $\cos{\frac{2\pi}{7}}\notin\mathbb{Q}$? Dec16 accepted Why is this unbounded linear functional also has a closed kernel? Dec11 accepted If a linear functional is not bounded, then it has a non-closed kernel. Jun26 accepted Is convergence in $I^I$ topology equivalent to point-wise convergence? Jun17 accepted Does a nonnegative real matrix always have a nonnegative eigenvector? May20 accepted Why the root of this tree has to be “1”? Feb26 accepted What is the sufficient and necessary condition for $U$ and $V$ to be the same in the SVD? Dec17 accepted How is it that the derivative operator is a closed linear operator? Dec10 accepted Is the set of real numbers the largest possible totally ordered set? Nov28 accepted Do $e_1$, $e_2$, … generate the entire $l_2$ space? Nov25 accepted For what values of $\alpha$ does this integral converge? Oct23 accepted Tossing 10 coins, what's the easiest way to see that these two events are independent? Oct16 accepted What's the algorithm of finding the convex combination of permutation matrices for a doubly stochastic matrix? Oct7 accepted Is there a particular notation for a function confined in a set? Oct3 accepted Is this function sequence applicable for Arzelàâ€“Ascoli? Oct3 accepted How do I prove that if $A$ is positive definite, then it is invertible and $A^{-1}$ is also positive definite? Oct2 accepted Two questions for Hermitian matrices. Oct2 accepted Find all real numbers $t$ such that the quadratic form $f$ is positive definite.