Operator Decomposition via Total Sequences in Hilbert Spaces

Abstract: We investigate the structure of total sequences in complex Hilbert spaces and construct explicit representations of the identity operator as a series of rank-one operators. Given a total sequence ${v_n}{n\in\mathbb{N}} \subseteq \mathcal{H}$, we establish the existence of sequences ${w_n}, {z_n} \subseteq \mathcal{H}$ and a monotonic function $\varphi: \mathbb{N} \to \mathbb{N}$ with $\varphi(n) \leq n$, such that $z_n$ lies in the span of ${v_k: k \geq \varphi(n)}$ and $\mathrm{id}{\mathcal{H}} = \sum{n=1}^\infty w_n z_n^*$ converges in the strong operator topology. Our proof combines orthogonal decomposition techniques, separability arguments, and Neumann series methods to construct a global operator identity from local approximations. This contributes to the understanding of total sequences and their role in operator-theoretic constructions.