2 problems

Let $\Omega\subset\mathbb{R}^d$ be a compact subset, let $\mu$ be a finite measure on $\Omega$, and let $X_N$ be an $N$-dimensional subspace of the real space $L_2(\Omega,\mu)$ who…

Exact density-radius conjecture. There exist two particular, non-computed positive constants $C'$ and $D'$ such that