$\Delta \subset \Phi$ is a base in a root system imples $\Delta^\vee \subset \Phi^\vee$ is a base in a root system
103662
How to prove that $B^\vee$ is a base for coroots?
121100
Rootspaces are $\mathop{ad}$ nilpotent
28402
Number of bases of an n-dimensional vector space over q-element field.
56370
Associative operation on a set $S$
133266
If $(X, \mathcal{T})$ has a countable subbasis, then it has a countable basis
111191
Show that $P_i$ and $\sum_i P_i$ being idempotent implies $P_i P_j=\delta_{ij}$
152503
Rational numbers as vectors in infinite dimensional space with the basis $( \log 2,\log 3, \log 5, \log 7, \dots, \log p, \dots) $
146664
The union of two linearly independent subsets
132487
Proving that if $V$ is an inner product space and $U_1, U_2$ are subsets, then $U_1 \subset U_2$ if and only if $U^{\perp}_2 \subset U^{\perp}_1$
158582
Prove that $\{\frac{\phi (n)}{n}\}_{n \in \Bbb N}$ is dense in $[0,1]$
107765
Prove that there exists two roots in $[-1,1]$
43462
Disprove $\mathcal{P}(A\Delta B) \setminus \{\emptyset\} = \mathcal{P}(A) \Delta\mathcal{P}(B) $. Is my proof good?
5599
Proving an inclusion for the derived group
77791
Proving an inclusion related to algebraic sets and interpreting it
18527
Confusion on Derived Sets and the $n$-the Derived Set
52565
Prove that if $d \mid n \in \mathbb{N}$, then $\varphi(d) \mid \varphi(n)$.
113136
Generators of the ideal correspond to $d$-uple embedding