“…The study of differential equations [1,9,10,21] with causal operators [2-5, 7, 11-13, 19, 22-24] has a rapid development in the recent years and some results are assembled in a recent monograph [11]. The term of causal operators is adopted from engineering literature and the theory these operators has the powerful quality of unifying namely the fractional differential equations [2,11,14,15,24], ordinary differential equations [9,10], integro-differential equations [18], differential equations with finite or infinite delay, Volterra integral equations and neutral functional equations [3,11].…”