could you please help me in this matter
question Let $H$ be a Hilbert space and $B=\{e_{n}\}_{n \in \mathbb{N}} \subset H$ be a sequence of orthonormal vectors. Prove that $e_{n} \rightharpoonup 0$
I'm having trouble applying bassel inequality, because I do not know if we consider this normal sequence as a replacement only for the orthogonal system.
any help be welcome, thanks