Chiappinelli, Raffaele. “Rayleigh Quotient and Surjectivity of Nonlinear Operators in Hilbert Space”. Annals of Mathematics and Physics 7, no. 3 (September 28, 2024): 277–278. Accessed August 27, 2025. https://www.mathematicsgroup.com/amp/article/view/AMP-7-232.