Wang Xiaoming invented eight pairwise connected regions with genus 2:
P is the number of holes. When p=2. N2=8 .
The picture on the right is folded in half up and down, then folded in half left and right to form a torus, and then the pipes of 7 and 8 are installed in corresponding positions, which is an 8-shaped torus.
4. We construct nine pairwise connected regions in Genus 3, in which N3=9.
Fold the above picture in half up and down, then fold it in half left and right to form a ring, and then install the trident in the corresponding position, that is, nine areas with three holes are connected in pairs.