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2. Algebraic topology and elliptic operators;Atiyah;Comm. Pure Appl. Math.,1967
3. Systems of integral equations on a half-line with kernels depending on the difference of arguments;Gohberg;Amer. Math. Soc. Transl.,1960
4. P. R. Halmos, “A Hilbert Space Problems Book,” p.143, Van Nostrand, Princeton, N.J.
5. L. Hormander, “An Introduction to Several Complex Variables,” pp. 44–46, Van Nostrand, Princeton, N. J.