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4h
comment Proofs that rely on an infinite matrix
If $\mathcal H$ is a separable Hilbert space, then this is O.K. since such a space has a countable basis. If this basis is $(e_i)$ then $\langle Ae_i,e_j \rangle$ determines $A$ completely. This is even for uncountable bases true if we require that $\langle A\phi, \psi \rangle$ is known for all $\phi,\psi \in \mathcal H$.
5h
answered Projection is an open map
6h
comment Is $\ell^1$ an inner product space?
I think you are missing some squares in your parallelogram law.
6h
comment dominated convergence theorem and solve an integral
Are there no restrictions for $a$ and $b$ ? If you take $a =1$ and $b = 0$ the integral is $1$ but the sum does not converge.
6h
answered Product of bounded and convergent to $0$ sequence is a convergent to $0$ sequence
2d
awarded  Popular Question
Oct
18
comment $B$-tight frame (Tao and Kadison Singer)
Thanks. So I think that it is useful to do all computations in this eigenbasis of $\mathbb C^d$.
Oct
18
accepted $B$-tight frame (Tao and Kadison Singer)
Oct
18
comment Limit Superior and Limit Inferior of sequence
For example for $(i)$: To prove $(a)$ let $\epsilon > 0$. Then $U< U + \epsilon$ and hence there is some $N \in \mathbb N$ with $\sup_{n \geq N} a_n < U + \epsilon$. This means for all $n \geq N$ that $a_n \leq \sup_{n \geq N} a_n < U + \epsilon$.
Oct
18
comment Limit Superior and Limit Inferior of sequence
Maybe you can show that all these conditions are equivalent to $\limsup a_n = \inf_{n\in \mathbb N} \sup_{m \geq n} a_m$
Oct
18
revised $B$-tight frame (Tao and Kadison Singer)
edited title
Oct
18
asked $B$-tight frame (Tao and Kadison Singer)
Sep
26
accepted Coproduct in category of pointed spaces
Sep
26
awarded  Yearling
Sep
26
comment Coproduct in category of pointed spaces
No, I am not. .
Sep
26
asked Coproduct in category of pointed spaces
Sep
18
comment Intersection of two equally long lines in a set with diameter $1$
Thanks. I just had the same idea now.
Sep
18
accepted Intersection of two equally long lines in a set with diameter $1$
Sep
18
asked Intersection of two equally long lines in a set with diameter $1$
Jul
24
comment Division with Remainder
$48 \equiv 0 \mod 12$ should also be the result of your calculator.