I have one surface and two curves. I want to split the surface into three parts with these curves. But I don’t know why in my GH there are always only two parts (0-Trimmed surface and 1-Trimmed surface)?

Can’t read your R6 .3dm file in R5, can you internalize your geometry into the GH file?

Also, due to the intentional incompatibility of R5 and R6, the Subtract component is missing from your GH file…

I tried substituting an arbitrary rectangle for the surface but the code failed at the CCX component. The Python isn’t helpful either, and probably not necessary?

The two new components you’ll require are Unit Z and Construct Plane. Connect the T (Tangents) output of the Divide Curve component to the upper List Item component to get the curve tangents that correspond to the points that you’ve picked, then use the points, the tangent vectors and the world Z direction to construct the planes.

Hopefully this description, along with the screenshot above, will help you figure this out!