cinema4D - Use Boole Object with Extruded Spline

Background

I drew a letter (that's about as far as my drawing skills go) by hand using the Freehand Spline tool and extruded it using the Extrude Nurbs.

Now as you can see the letter is a P and so I need to subtract the center of it. Therefore I want to use the Boole tool subtracting a little spline (extruded as well) from the large P. Here are my splines:

I added P and pSub to the Bool and set it to A subtract B (which works when using a normal cube and a sphere for example). Now the result is not any different from the top picture, A does not subtract B.

Note

The center little spline is longer than the outer one (the objects are laying –> ”longer“ as in the y-value being higher).

Question

Is there a way to fix this and to cut out pSub from P so that it is an actual P?

The bool-object only works with polygonal geometry. Simply select both splines in the object-manager and do a right-click. In the context-menu there is an option like 'combine and delete' or 'merge and delete' (i am using a german version) that combines the selected objects into a single one and deletes the base-objects. Depending on the complexity of the resulting spline you may have to deactivate the automatic creation of top-surfaces in the extrude-object and fill the holes manually using the 'fill-polygon-hole'-tool.

Second approach: extrude both splines individually first (creating polygonal geometry) and use a bool on the extruded objects.

IMHO the first approach is a more 'clean'-way to solve your problem.