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

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

(ξ2, η2,σ) such that

ξ1 = ζ − n m + n

δ, η1 = ζ + m m + n

δ;

ξ2 = ζ + n m + n

δ, η2 = ζ − m m + n

δ

for some ζ and δ.]