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Jan
10
accepted Is there a name for a monoid with a distinguished absorbing element?
Dec
12
accepted What does the theory of the empty set look like?
Nov
21
accepted Why is the union of two closed sets again closed in the Scott topology?
Jul
19
accepted Are there noncontinuous derivations $C^1(X) → ℝ$?
Jul
5
accepted Characterization of the space of integrable functions stable under multiplication
Jun
14
accepted Justifying the integral identity “$\int \mathrm{e}^{cx} \sin bx\, \mathrm{d}x = \frac{\mathrm{e}^{cx}}{b^2 + c^2}(c \sin bx - b \cos bx)$”
May
23
accepted Are binomial series multiplicative in their bases?
Apr
8
accepted Why are functors exact if they preserve all short exact sequences?
Apr
8
accepted The pushout of an open/closed injective map is open/closed
Mar
15
accepted Can the cohomology ring of the two-fold torus be calculated abstractly?
Feb
1
accepted Extending homotopies to contract an ascending union of contractible spaces
Jan
31
accepted Which maps on the zeroth homology do actually come from continuous maps?
Jan
29
accepted Is reduced homology a full functor on connected spaces?
Jan
27
accepted How is induction justified in intuitionistic logic?
Dec
29
accepted Equivalent characterizations of group objects
Dec
14
accepted Are the polynomial functions on $S^1$ dense in $C(S^1,ℂ)$?
Dec
14
accepted Can $ℂ$ be viewed as a (nontrivial) field of fractions?
Nov
29
accepted Why is every category in which all (even large) limits and colimits exist thin?
Nov
6
accepted Is a set open in a product of spaces if all its segments are open in their factors?
Oct
27
accepted Does $f ≥ g$ always imply $f^{-1} ≤ g^{-1}$ for invertible $f, g$?