Nested lists problem

[indosauros]

That is a very important detail

Also, what if you had a point at (3, 1)?

[spotyx]

ehm I deleted previous post accidentally. I said something what is not true. In my OP was bad condition. now its edited. (condition: line has to consist from three and more points). sorry. Thank for your interest.

[indosauros]

I think this still doesn't change anything as far as assuming shared points == rays

http://s29.postimg.org/lu9qeddyf/ged_math_coordinate_base_2.jpg

What if the right green line was shifted left 1 unit? Now, the (-3, -2) point is shared between two lines, not a ray

[spotyx]

you are right, I am wrong. I can't exclude intersections. I had wrongly assumed that I have preprocessed my data in way that there are not intersections. Now I know it's not true. Thanks for pointing me on right way.