Invertibility of multipliers and the spectrum of an operator in spaces with different norms

I. Ya. Shneiberg, Mat. Issled.,9, No. 2, 214–229 (1974). L. Hörmander, Estimates for Operators Invariant under a Shift [Russian translation], Inostr. Lit., Moscow (1962). S. Igari, Tohoku Math. J.,21, 304–320 (1969). I. C. Gohberg and N. Ya. Krupnik, Introduction to the Theory of One-Dimensional Singular Operators [in Russian], Kishinev (1973). N. Aronszajn and E. Gagliardo, Ann. Mat. Pure Appl.,68, 51–118 (1965).