1. The positive surface is for tracking one midpoint for coordinates A and B
2. The negative surface is for tracking another midpoint for coordinates C and D
Together it's a klein bottle. Klein bottle's always intersect, so therefore there's always an intersection of the two midpoints, which is why there's a set of points A, B, C and D such that line segments A and B are equally long as C and D going through the same midpoint.
1. The positive surface is for tracking one midpoint for coordinates A and B
2. The negative surface is for tracking another midpoint for coordinates C and D
Together it's a klein bottle. Klein bottle's always intersect, so therefore there's always an intersection of the two midpoints, which is why there's a set of points A, B, C and D such that line segments A and B are equally long as C and D going through the same midpoint.