“…and by(3.8), joint with (3.6), we get 0 ≤ w(a + ) ≤ w(a) ≤ 0. If τ > a, then, by definition of τ , w(τ − ) ≤ 0.Using (3.8) joint with (3.5) and (3.6), we also have 0 ≤ w(τ + ) ≤ w(τ − ) ≤ 0, and the claim is proved.Therefore, since w(τ ) = 0, (3.4) reads as follows: for every s ∈ (τ, t 0 ) we havew(s) ≤ L ˆs τ w(ρ) dρ.By the integral form of the Gronwall inequality (see for instance[22, Lemma 3.2], which is a particular case of [23, Theorem 3.1]) , we get w ≤ 0 in [τ, t 0 ], which is in contradiction with (3.7).…”