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Jul
26
accepted On the importance of natural transformations
Jul
6
accepted What's the name given to the ratio $P^2/A$ for a closed figure in the Euclidean plane?
Jul
5
accepted Looking for elementary proof of “for a circle, $C^2/A = 4 \pi$”
May
26
accepted Looking for a “Guide for the Perplexed by Low-dimensional Topology”
May
25
accepted Looking for student's guide to diagram chasing
Jan
3
accepted When is a pullback also a pushout?
Apr
7
accepted How to recognize adjointness?
Apr
5
accepted What are integrating factors, really?
Mar
16
accepted On proving $n = \sum_{d\mid n}\varphi(d)$
Mar
16
accepted On last digit of 4 consecutive primes less than 10 apart
Mar
16
accepted Is there any advantage to the $a \equiv b\;\;(\mathrm{mod}\;c)$ notation?
Mar
3
accepted Natural uses for the co-product of sets?
Feb
2
accepted Looking for counterexample where $K \not \subset H$ and $[G:K] \neq [H:H\cap K]$
Feb
1
accepted How to prove $\frac{1}{q} \binom{p^k q}{p^k} \equiv 1 \mod p\;\;$?
Jan
19
accepted Why isn't the orbit-stabilizer theorem obvious?
Jan
11
accepted What's the rationale for requiring that a field be a $\boldsymbol{non}$-$\boldsymbol{trivial}$ ring?
Jan
8
accepted Matrix-free proof of $Z(GL_n(F)) = \{\lambda I:\lambda \in F^\times\}$?
Jan
7
accepted Simpler proof of $g\,h\,g^{-1} = h^a \Rightarrow g^n\,h\,g^{-n} = h^{a^n}$
Jan
2
accepted Simple proof that symmetries of regular polyhedron fix its center?
Dec
26
accepted Looking for simpler proof of “well-definedness” of basis subtended by points in “general position”