“…Proof of Theorem 6 We assume without loss of generality that f is strictly concave on [a, c] and strictly convex on [c, b]. The following relations hold true for every arbitrarily fixed u, v ∈ (c − ε, c) ∩ (a, b), u < v and w, z ∈ (c, c + ε) ∩ (a, b), w < z:…”