with each of the sets consisting of two points (1, 1, ), (2, 2, ) such

with each of the sets Ω∆ consisting of two points (ξ1, η1, σ),

(ξ2, η2, σ) such that

ξ1 = ζ − n m + nδ, η1 = ζ + m m + nδ;

ξ2 = ζ + n m + nδ, η2 = ζ − m m + nδ

for some ζ and δ.]