MYSHKIS, A.; BAINOV, D.; DIMITROVA, M. Oscillatory and Asymptotic Properties of the Solutions of a Class of Operator-Differential Equations. Revista Matemática Complutense, v. 7, n. 2, p. 309, 1 ene.1994 https://doi.org/10.5209/rev_REMA.1994.v7.n2.17747.