Create a patch surface out of a collection of curves and points.

Input parameters:

1. Cr → Boundary and interior curves to patch.
2. Pt → Optional points to coincide with the patch.
3. Sp → Number of spans of the patch surface.
4. Fx → Flexibility of the surface in areas with few or distant constraints. Flexibility must be between zero (most stiff) and ten (most flexible).

Output parameters:

1. Sf → Surface constructed out of the curves and points.