Let n = 2k and k ≥ 2. We already know that χ¯vef (Wn) ≥ 5. To show that χ¯vef (Wn) ≤ 5, it suffices to colour the central
vertex and the outer face with colour 1. The edges incident with the central vertex are coloured alternately with colours 2
and 3, and similarly uncoloured vertices alternately with colours 2 and 3, too, in such a way, that vertex incident with the
edge coloured with 2 is assigned 3 and vice versa. Analogously, it suffices to colour faces incident with central vertex and
remaining edges with colours 4 and 5.