• [1] Peter D. Lax, On Cauchy’s problem for hyperbolic equations and the differentiability of solutions of elliptic equations, Comm. Pure Appl. Math. 8 (1955), 615–633. MR 0078558, https://doi.org/10.1002/cpa.3160080411
• [2] Lars Hörmander, On the theory of general partial differential operators, Acta Math. 94 (1955), 161–248. MR 0076151, https://doi.org/10.1007/BF02392492
• [3] N. I. Achieser and I. M. Glasmann, Theorie der linearen Operatoren im Hilbert-Raum, Akademie-Verlag, Berlin, 1954 (German). MR 0066560
• [4] G. C. Rota, Extension theory of differential operators. I, Comm. Pure Appl. Math. 11 (1958), 23–65. MR 0096852, https://doi.org/10.1002/cpa.3160110103
• [5] I. C. Gohberg and M. G. Kreĭn, Systems of integral equations on a half line with kernels depending on the difference of arguments, Amer. Math. Soc. Transl. (2) 14 (1960), 217–287. MR 0113114
• [6] Frigyes Riesz and Béla Sz.-Nagy, Functional analysis, Frederick Ungar Publishing Co., New York, 1955. Translated by Leo F. Boron. MR 0071727

Bibliography

[1]

P. D. Lax, On Cauchy's problem for hyperbolic equations and the differentiability of solutions of elliptic equations, Comm. Pure Appl. Math. 8 (1955), 615-633. MR 0078558 (17:1212c)

[2]

L. Hörmander, On the theory of general partial differential operators, Acta Math. 94 (1955), 161-248. MR 0076151 (17:853d)

[3]

N. I. Achiezer and I. M. Glasman, Theorie der linearen Operatoren im Hilbert-Raum, Akademie-Verlag, Berlin, 1954. MR 0066560 (16:596f)

[4]

G. C. Rota, Extension theory of differential operators. I, Comm. Pure Appl. Math. 11 (1958), 23-65. MR 0096852 (20:3334)

[5]

I. C. Gohberg and M. G. Krein, Systems of integral equations on a half line with kernels depending on the difference of arguments, Amer. Math. Soc. Transl. (2) 14 (1960), 217-287. MR 0113114 (22:3954)

[6]

F. Riesz and B. Sz. Nagy, Functional analysis, Ungar, New York, 1955. MR 0071727 (17:175i)