Justification of the averaging method for functional-differential equations with maximums. Bainov, D.D., Milusheva, S.D. (1985) Publications de l'Institut Mathématique. Nouvelle Série
Justification of the averaging method for multipoint boundary value problems for a class of functional-differential equations with maximums. S. D. Milusheva, D. D. Bainov (1986) Collectanea Mathematica