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Kharakhanian, I. M. ON THE EQUATION ${\bf{\it h}}x-x{\bf{\it k}}=c$ IN BANACH ALGEBRA ${\bf{\it A}}$, WITH HERMITIAN COEFFICIENTS ${\bf{\it h}}, {\bf{\it k}}$. Proc. YSU A: Phys. Math. Sci. 2002, 36 (1 (197), 3-8. https://doi.org/10.46991/PYSUA.2002.36.1.003.