“…It is easy to verify that B T pAq tTpα 1 , α 2 , α 3 q : pα 1 , α 2 , α 3 q Au is a convex set. Indeed, B is a triangle (see Figure 2) with vertices P 1 T p1, 0, 0q p∆ A 1 pθ 1 q, ∆ A 2 pθ 1 q, ∆ A 3 pθ 1 qq, P 2 T p0, 1, 0q p∆ A 1 pθ 2 q, ∆ A 2 pθ 2 q, ∆ A 3 pθ 2 qq and P 3 T p0, 0, 1q p∆ A 1 pθ 3 q, ∆ A 2 pθ 3 q, ∆ A 3 pθ 3 qq (these points are not aligned owing to the restrictions on the quantities ∆ A i pθ j q, [14]). Now, we turn to the main argument of the proof.…”