The invention notably relates to a method for determining specifications of the input of a manufacturing operation that outputs a part having cut-outs. The method comprises providing specifications of the output part, including a user-designed B-Rep having cycles of edges and modeling the part, the cut-outs being represented by the user with tunnels in the B-Rep, determining the set that consists of all cycles being the one having the smallest length in a respective equivalence class, performing a process on the set that includes iterating replacing a cycle when this reduces the length, and deleting a cycle when a sum results in a boundary cycle, otherwise replacing the cycle by the sum when this reduces the length.The invention offers an improved solution to detect, in a B-Rep having cycles of edges and modeling a part having cut-outs represented by tunnels, location of at least part of the tunnels.