I was experimenting impasses and I found this about spiral chains:

- Consider all possible maps less than or equal to 18 faces (including the ocean)
- Do not consider duplicates (isomophic maps)
- There is still a very large number of possible such maps
- Remove all maps that have faces with 2, 3, 4 edges
- These maps, as found by Kempe back in 1879, can be not considered
- See http://en.wikipedia.org/wiki/Four_color_theorem:
- “Kempe also showed correctly that
*G*can have no vertex of degree 4″

- “Kempe also showed correctly that

- See http://en.wikipedia.org/wiki/Four_color_theorem:

- These maps, as found by Kempe back in 1879, can be not considered
- The number of maps reduces to 22 maps only
- All these 22 maps have only one spiral chain
- To get the Tait coloring, required me only one Kempe chain color swapping per map
- Actually I complitely colored the spiral (the backbone) with two colors and then I finished the other edges and at the end I worked on impasses
- Next, I’ll try the algorithm described here:

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