Find all surface edges which are linear within tolerance.

Input parameters:

1. Sf → Surface for edge search.
2. L- → Lower deviation limit. When the lower limit exceeds the upper limit, linearities that fall between the limits are omitted instead.
3. L+ → Upper deviation limit. When the upper limit is smaller than the lower limit, linearities that fall between the limits are omitted instead.

Output parameters:

1. Cr → Found edge curves.
2. Ix → Found edge indices.