Remove duplicated lines - sphere definition

I have a sphere meshed with triangles. I get a list of all unique lines constructing the mesh. With my code I still get duplicates. What’s the reason? What should I change?

Is it because of precision? Or python sets don’t work with points?

180507_Dome.dyn (17.2 KB)

Could be precision or it could be curve direction. LineAB != LineBA.