An orthonormal sequence of vectors vii∈N{v_i}_{i\in\mathbb N}vii∈N in a Hilbert space HHH is an orthonormal (Hamel) basis for HHH if h=∑i∈N⟨vi,h⟩vih = \sum_{i\in\mathbb N} \langle v_i, h\rangle v_ih=i∈N∑⟨vi,h⟩vi for all h∈Hh \in Hh∈H.
Wikidata ID: Q189569