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17h
accepted Possible angles between roots in a root system
18h
asked Possible angles between roots in a root system
May
24
comment Rootspace decomposition of a Lie algebra
I am reading Humphreys, too but I do not immediately see why the sum is direct.
May
23
accepted Stone-Čech compactification of discrete space
May
23
asked Rootspace decomposition of a Lie algebra
Apr
21
comment Should an object in the category always be a formal mathematical structure?
Maybe you shoud first try to read articles over ZFC, such as here en.wikipedia.org/wiki/Zermelo%E2%80%93Fraenkel_set_theory. Furthermore you can't define something to be large. For example the category of sets and functions between them is not small since the objects do not form a set. (There can't be the set of all sets.) So the objects form a so called class, and hence the category of sets is large.
Apr
21
comment Should an object in the category always be a formal mathematical structure?
Maybe you are looking for the difference between small and so called large categories. In small categories the objects form really a set and also the morphisms between objects form sets. Besides that you can always define categories which are not related to any popular mathematical structure, of course.
Apr
16
comment $2D$ plane geometry inequality
Then, indeed all points above the line you drawed. (including the line itself)
Apr
16
answered $2D$ plane geometry inequality
Apr
16
comment Is a subspace of functions that essentially depend only on one variable closed?
I guess he means the functions $f$ which are equal, when hold constant in the second variable.
Apr
16
revised Graph Theory Matchings
latex added
Apr
16
suggested approved edit on Graph Theory Matchings
Apr
16
accepted Finite union of compact sets is compact
Apr
13
comment What is the reverse image of $f:[0,6\pi] \rightarrow \mathbb{R}$, $f = sinx$?
The reverse image is a group ?
Apr
10
comment Is a closed convex set $E$ in $\mathbb{R}^n$ equal to the closure of its interior?
I just added the link. Sorry.
Apr
10
comment Is a closed convex set $E$ in $\mathbb{R}^n$ equal to the closure of its interior?
There is a theorem wich states that a compact convex set is the convex hull of its extreme points. See en.wikipedia.org/wiki/Krein%E2%80%93Milman_theorem
Apr
10
answered Prove that if $m$ and $n$ are integers and $mn$ is even, then $m$ is even or $n$ is even.
Apr
9
comment Existence of bijection that reorders elements?
Edit is ok, I guess. Then just ignore my answer :)
Apr
9
answered Existence of bijection that reorders elements?
Apr
9
answered why union and Cartesian product of infinitely many compact sets is not compact