2 problems

Let $H$ be a Hilbert space, let $\mathcal{M}=(m_n)$ be a sequence of scalars, and let $\mathcal{X}={x_n}$ and $\mathcal{Y}={y_n}$ be sequences in $H$. Balazs–Stoeva conjecture. The…

Let ${\cal H}$ be a Hilbert space and let $M_{m,\Phi,\Psi}$ be a multiplier associated with scalar sequence $m$ and sequences $(\phi_n)$ and $(\psi_n)$ in ${\cal H}$. Let…