Description: The lexicographical ordering for points in the two dimensional Euclidean
plane: a point is less than another point iff its first coordinate is
less than the first coordinate of the other point, or the first
coordinates of both points are equal and the second coordinate of the
first point is less than the second coordinate of the other point:
<. a , b >. <_ <. x , y >. iff
( a < x \/ ( a = x /\ b <_ y ) ) . (Contributed by AV, 12-Mar-2023)