2025/05/21 by Prokofyev, Mikhail
#FOS: Mathematics #Functional Analysis (math.FA)
paper · doi:10.48550/arxiv.2505.15321
In this paper, we study the property of hereditary completeness of vector systems \xk\k=1^∞ in a Hilbert space. A criterion of hereditary completeness is obtained in terms of projectors on closed linear spans of systems of the form \xk\k ∈ N, N ⊂ ℕ. Developed technique has been used to prove that mixed systems of a hereditarily complete system are also hereditarily complete. In conclusion, the problem of possible defects in a nonhereditarily complete system is considered.