“…Concerning the controllability problem, due to the infinite-dimensional nature of the dynamics of neutral functional differential equations and difference equations, several different notions of controllability can be used, such as exact, approximate, spectral, or relative controllability [5,30]. Relative controllability has been originally introduced in the study of control systems with delays in the control input [5,20,27], but this notion has later been extended and used to study also systems with delays in the state [13,29] and in more general frameworks, such as for stochastic control systems [19] or fractional integro-differential systems [2]. The main idea of relative controllability is that, instead of controlling the state x t : [−r, 0] → C d of (1.1), defined by x t (s) = x(t + s), in a certain function space such as C k ([−r, 0], C d ) or L p ((−r, 0), C d ), where r ≥ max j∈ 1,N Λ j , one controls only the final state x(t) = x t (0).…”