Moslehian, Mohammad Sal, and Ali Zamani. “Mappings Preserving Approximate Orthogonality in Hilbert $C^*$-Modules”. Mathematica Scandinavica 122, no. 2 (April 8, 2018): 257–276. Accessed July 24, 2026. https://journals.msp.org/mscand/article/view/279.