“…The assumptions above, especially (F3),(F4), are inspired by the real-life model describing evolution of dislocation density, see [8,11,18,19,20,22] for detailed description and discussion of the DDE involved. In Lemma 3.1 below we prove that under the assumptions (F1)-(F3) the equation (1.1) has unique solution z = z(t) on the whole interval [−τ, (n + 1)τ ].…”